Toxicology – Selected Antiviral Drugs

Core Concept

This older chapter combines several pharmacologically unrelated antiviral drugs:

• Acyclovir / valacyclovir
• Famciclovir
• Amantadine / rimantadine
• Cidofovir
• Foscarnet
• Ganciclovir / valganciclovir
• Ribavirin

They do not produce a common antiviral toxidrome. Toxicity is best remembered by the characteristic organ injury of each drug:

• Acyclovir/valacyclovir → crystal nephropathy + neurotoxicity
• Amantadine → CNS + cardiac toxicity
• Cidofovir → proximal tubular nephrotoxicity/Fanconi syndrome
• Foscarnet → nephrotoxicity + major electrolyte disturbances
• Ganciclovir/valganciclovir → bone-marrow suppression + renal accumulation
• Ribavirin → hemolytic anemia

There is no universal antidote for this group.

1. Acyclovir and Valacyclovir

Acyclovir inhibits viral DNA polymerase after activation within infected cells.

Valacyclovir is the oral prodrug of acyclovir and has substantially greater oral bioavailability.

Famciclovir is similarly converted to the active antiviral penciclovir.

Acute uncomplicated oral overdose is often mild, but excessive systemic exposure—especially with renal dysfunction—can cause important renal and neurologic toxicity.

Acyclovir Crystal Nephropathy

Acyclovir has limited urinary solubility.

High tubular concentrations can result in:

Acyclovir precipitation → intratubular obstruction → crystal nephropathy → AKI

Risk is greatest with:

• High systemic exposure
• Rapid IV administration
• Dehydration
• Preexisting renal impairment
• Inadequate dose adjustment

Clinical Features of Acyclovir Nephrotoxicity

Possible findings include:

• Rising creatinine
• Reduced urine output
• Hematuria
• Crystalluria
• Flank discomfort
• AKI

Renal dysfunction then reduces acyclovir elimination, potentially increasing systemic exposure further.

Acyclovir/Valacyclovir Neurotoxicity

Accumulation can cause:

• Confusion
• Agitation
• Hallucinations
• Tremor
• Myoclonus
• Dysarthria
• Ataxia
• Somnolence
• Seizures
• Coma

The risk is particularly important in patients with renal impairment.

Acyclovir Neurotoxicity vs Viral Encephalitis

This distinction can be difficult because acyclovir is often being administered specifically for suspected CNS herpes infection.

Features favoring drug accumulation include:

• Development after acyclovir/valacyclovir exposure
• Renal dysfunction
• Myoclonus or prominent neuropsychiatric abnormalities
• Improvement after withdrawal and clearance of the drug

However, these findings are not sufficiently specific to exclude active viral encephalitis.

Clinical context, CSF studies, imaging, renal function, and treatment history must be integrated.

Acyclovir Management

Important measures include:

• Stop or appropriately reduce further exposure
• Correct dehydration when present
• Monitor renal function and urine output
• Avoid additional nephrotoxins
• Adjust future dosing for kidney function
• Treat neurologic complications supportively

Routine forced diuresis is inappropriate.

Hemodialysis and Acyclovir

Acyclovir is substantially dialyzable.

Hemodialysis can be useful in selected patients with:

• Severe renal failure
• Marked drug accumulation
• Severe or persistent neurotoxicity

It is not routinely required after a minor ingestion with normal renal function.

2. Famciclovir

Famciclovir is converted to penciclovir.

Acute overdose experience is limited, but uncomplicated exposures generally produce relatively mild effects such as:

• Nausea
• Headache
• GI discomfort
• Dizziness

Because active drug is eliminated renally, renal dysfunction can increase exposure.

Severe toxicity is considerably less characteristic than with drugs such as amantadine or foscarnet.

3. Amantadine

Amantadine deserves separate attention because its toxicity is substantially different from that of nucleoside antiviral agents.

Although historically used against influenza A, amantadine is no longer recommended for routine influenza treatment because of widespread viral resistance.

It remains clinically relevant primarily for neurologic indications such as Parkinsonian syndromes and drug-induced movement disorders.

Amantadine Toxicity

Amantadine overdose can produce severe:

• CNS excitation or depression
• Delirium
• Hallucinations
• Seizures
• Cardiac conduction abnormalities
• Ventricular dysrhythmias

It also has antimuscarinic-like properties.

Antimuscarinic Features

Possible findings include:

• Mydriasis
• Dry mouth
• Tachycardia
• Reduced bowel motility
• Urinary retention
• Agitation
• Hallucinations
• Hyperthermia

However, amantadine poisoning should not be reduced to a pure anticholinergic syndrome because cardiac and neurologic toxicity can dominate.

Cardiotoxicity

Severe amantadine poisoning can produce:

• Tachycardia
• QRS abnormalities
• QT abnormalities
• Ventricular ectopy
• Ventricular tachyarrhythmias
• Hypotension
• Cardiac arrest

Electrolyte disturbances can worsen electrical instability.

Hypokalemia

Hypokalemia has been described in severe amantadine poisoning and can contribute to ventricular dysrhythmias.

Therefore significant poisoning warrants careful monitoring of:

• Potassium
• Magnesium
• ECG

Amantadine and Renal Function

Amantadine is predominantly eliminated through the kidneys.

Renal impairment can therefore produce substantial accumulation even during apparently conventional treatment.

Older adults with declining kidney function are particularly vulnerable to:

• Hallucinations
• Confusion
• Myoclonus
• Delirium
• Other CNS toxicity

Amantadine Withdrawal

Abrupt discontinuation after chronic use can occasionally produce a withdrawal syndrome with:

• Delirium
• Agitation
• Worsening Parkinsonism

Rare severe syndromes resembling neuroleptic malignant syndrome have also been reported.

This is distinct from acute amantadine overdose.

Rimantadine

Rimantadine is another adamantane antiviral historically used for influenza A.

Because of widespread resistance, it is also no longer recommended for routine influenza therapy.

Its toxicity can include:

• CNS effects
• Antimuscarinic-like findings
• GI symptoms

Severe cardiac toxicity is generally more strongly associated with amantadine.

Physostigmine – Important Update

The older recommendation to consider physostigmine broadly for severe amantadine toxicity requires substantial caution.

Amantadine overdose can involve:

• QRS/conduction abnormalities
• Ventricular dysrhythmias
• Seizures

Therefore physostigmine is not a routine antidote.

It should only be considered in highly selected predominantly antimuscarinic delirium after ECG and seizure-risk assessment and with expert toxicology guidance.

Dialysis and Amantadine

Despite renal elimination, conventional hemodialysis removes relatively little amantadine because of its pharmacokinetic characteristics.

Thus the older claim that dialysis meaningfully lowers amantadine concentrations is misleading.

Management is primarily supportive.

4. Cidofovir

Cidofovir is a nucleotide analog historically important in treatment of selected severe viral infections, particularly CMV in immunocompromised patients.

Its defining toxicity is:

Dose-dependent proximal tubular injury

Cidofovir Nephrotoxicity

Proximal tubular dysfunction can produce:

• Rising creatinine
• Proteinuria
• Glycosuria despite normal blood glucose
• Phosphate wasting
• Bicarbonate wasting
• Electrolyte abnormalities
• Fanconi syndrome
• AKI

Cidofovir Risk Factors

Risk increases with:

• Preexisting renal dysfunction
• High exposure
• Other nephrotoxic drugs
• Inadequate renal-protective measures

Renal function and urinalysis are central to monitoring.

Probenecid and Cidofovir

Probenecid reduces active tubular uptake of cidofovir and is used with IV cidofovir to reduce nephrotoxicity.

Hydration is also part of standard nephroprotection.

However, probenecid should be understood primarily as a preventive component of prescribed cidofovir therapy, not as a universally established antidote after an overdose has already occurred.

5. Foscarnet

Foscarnet directly inhibits viral DNA polymerase without requiring intracellular phosphorylation.

Its major toxicities are:

• Nephrotoxicity
• Electrolyte disturbances

These can interact to produce severe neurologic and cardiac complications.

Foscarnet Nephrotoxicity

Foscarnet can cause:

• Rising creatinine
• Reduced GFR
• AKI
• Renal tubular dysfunction

Risk increases with:

• Dehydration
• High exposure
• Preexisting renal dysfunction
• Other nephrotoxins

Adequate hydration and renal dose adjustment are important during therapy.

Foscarnet Electrolyte Toxicity

Foscarnet can chelate divalent cations and disturb mineral metabolism.

Possible abnormalities include:

• Hypocalcemia
• Hypomagnesemia
• Hypokalemia
• Hypophosphatemia
• Sometimes hyperphosphatemia

Clinical Effects of Hypocalcemia

Patients may develop:

• Perioral tingling
• Paresthesias
• Muscle cramps
• Tetany
• Seizures
• QT prolongation
• Dysrhythmias

Ionized calcium can be particularly useful because total serum calcium may not accurately reflect the physiologically active fraction.

Foscarnet Monitoring

Significant toxicity warrants:

• Creatinine
• Potassium
• Magnesium
• Calcium, preferably ionized when clinically relevant
• Phosphate
• ECG

Correct clinically important electrolyte abnormalities carefully.

Dialysis and Foscarnet

Foscarnet can be removed to some extent by dialysis, but evidence supporting extracorporeal treatment specifically for overdose remains limited.

Renal replacement therapy should be considered according to:

• Renal failure
• Severe electrolyte abnormalities
• Conventional dialysis indications
• Overall clinical toxicity

6. Ganciclovir and Valganciclovir

Ganciclovir inhibits viral DNA synthesis and is particularly important against CMV.

Valganciclovir is its orally bioavailable prodrug and should be included in a modern discussion.

The defining toxicity is:

Bone-marrow suppression

Ganciclovir Hematologic Toxicity

Possible abnormalities include:

• Neutropenia
• Thrombocytopenia
• Anemia
• Pancytopenia

Severe neutropenia increases the risk of serious infection.

This toxicity is particularly important during prolonged therapeutic exposure.

Ganciclovir and Renal Function

Ganciclovir is substantially renally eliminated.

Renal impairment increases drug exposure and therefore increases the risk of:

• Marrow suppression
• Neurologic toxicity

Dose adjustment according to renal function is essential.

Ganciclovir Neurotoxicity

Less commonly, excessive exposure can cause:

• Confusion
• Tremor
• Seizures

A severe presentation warrants evaluation for renal accumulation and other neurologic causes.

Hemodialysis and Ganciclovir

Ganciclovir is dialyzable.

Dialysis may be useful in selected severe accumulation, particularly when renal failure is present.

Routine dialysis is not indicated after minor exposure.

7. Ribavirin

Ribavirin is a nucleoside analog with uses that have changed considerably since the older source.

Its most characteristic systemic toxicity is:

Hemolytic anemia

Ribavirin Hemolysis

Systemic ribavirin accumulates within erythrocytes and can produce oxidative/metabolic injury.

Possible findings include:

• Falling hemoglobin
• Fatigue
• Pallor
• Dyspnea
• Indirect hyperbilirubinemia
• Compensatory reticulocytosis

Patients with significant underlying cardiac disease may tolerate anemia poorly.

Aerosolized Ribavirin

The severe respiratory events described historically largely relate to specific clinical circumstances involving aerosolized therapy and severely ill infants.

They should not be generalized as the expected syndrome after an ordinary oral exposure.

Ribavirin and Pregnancy

Ribavirin has important embryotoxic and teratogenic potential.

Pregnancy-related precautions are particularly important because systemic ribavirin and its metabolites may persist for a prolonged period.

The old FDA pregnancy letter system is obsolete, but the reproductive risk remains clinically important.

Diagnosis

Because these drugs have very different toxicities, first identify the exact antiviral.

Acyclovir/valacyclovir

Focus on:

• Renal function
• Hydration
• Mental status

Amantadine

Focus on:

• Mental status
• ECG
• Potassium/magnesium
• Renal function

Cidofovir

Focus on:

• Creatinine
• Urinalysis
• Proximal tubular function

Foscarnet

Focus on:

• Renal function
• Calcium
• Magnesium
• Potassium
• Phosphate
• ECG

Ganciclovir/valganciclovir

Focus on:

• CBC
• Renal function

Ribavirin

Focus on:

• Hemoglobin
• Evidence of hemolysis

Laboratory Evaluation

Small uncomplicated exposures may require little or no testing.

For clinically important exposure, testing is agent specific rather than using one universal antiviral panel.

Possible studies include:

• CBC
• Glucose
• Electrolytes
• Creatinine/BUN
• Magnesium
• Calcium
• Phosphate
• Liver tests
• Urinalysis

ECG is particularly important for amantadine toxicity and significant foscarnet-associated electrolyte abnormalities.

Serum Antiviral Concentrations

Routine serum concentrations of these agents are generally not useful for emergency overdose management.

Clinical status, renal function, CBC, ECG, and electrolytes usually provide more actionable information.

Initial Management

General approach:

Airway/breathing → circulation → identify exact antiviral → determine renal function → ECG/electrolytes when indicated → evaluate CNS and hematologic toxicity → supportive care

Because several of these drugs are renally eliminated, renal function is particularly important.

GI Decontamination

Do not induce vomiting.

Ipecac has no modern role.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a substantial recent oral exposure when:

• The drug is adsorbable
• Airway protection is adequate
• Aspiration risk is acceptable
• Expected benefit justifies treatment

Many minor exposures need no GI decontamination.

Seizures

For toxicologic seizures:

Benzodiazepines are first-line.

Persistent seizures may require additional benzodiazepines, phenobarbital, or appropriate anesthetic therapy.

Always correct contributing abnormalities such as:

• Hypoglycemia
• Hypocalcemia
• Hypomagnesemia
• Hypokalemia
• Hypoxia
• Acid–base disturbance

This is particularly important with foscarnet.

Hyperthermia

If severe hyperthermia occurs:

• Control agitation/seizures
• Use active external cooling
• Correct dehydration and metabolic complications
• Monitor for rhabdomyolysis and organ injury

Antipyretics do not treat toxicologic hyperthermia unless fever from a hypothalamic set-point change is actually present.

The older term “malignant hyperthermia” should not be casually applied to amantadine toxicity.

Amantadine Dysrhythmias

Management should be based on:

• Rhythm
• QRS
• QT
• Potassium/magnesium
• Blood pressure
• Acid–base status

Avoid medications likely to worsen the existing conduction or repolarization abnormality.

The older blanket statement to avoid class IA drugs remains directionally reasonable, but modern management should be physiology- and ECG-directed rather than based on one antiarrhythmic class alone.

Enhanced Elimination – Summary

Acyclovir

Hemodialysis can meaningfully enhance elimination in selected severe accumulation.

Amantadine

Poorly removed by conventional hemodialysis; supportive care predominates.

Cidofovir

No routine extracorporeal antidotal strategy.

Foscarnet

Some dialysis removal is possible, but clinical overdose evidence is limited.

Ganciclovir

Dialyzable; may be useful in selected severe accumulation with renal dysfunction.

Ribavirin

Dialysis is not an effective routine antidotal strategy.

Monitoring and Observation

A universal 4–6 hour observation period is inappropriate.

Monitoring depends on:

• Exact antiviral
• Dose
• Route
• Symptoms
• Renal function
• ECG
• Electrolytes
• CBC
• Clinical trajectory

Some toxicities are delayed.

For example:

• Ganciclovir marrow suppression may evolve later.
• Ribavirin anemia is not excluded by a normal early hemoglobin.
• Acyclovir accumulation can persist when renal function is impaired.

Admission

Hospitalization may be appropriate for:

• Significant AKI
• Severe acyclovir neurotoxicity
• Amantadine delirium or seizures
• QRS/QT abnormalities
• Ventricular dysrhythmia
• Significant foscarnet electrolyte disturbances
• Symptomatic hypocalcemia
• Severe cytopenias
• Serious hemolytic anemia
• Persistent altered mental status
• Respiratory compromise
• Hemodynamic instability

ICU care is appropriate for malignant dysrhythmia, shock, status epilepticus, respiratory failure, or severe electrolyte-driven cardiac instability.

Pregnancy and Breastfeeding

The historical FDA pregnancy letter categories are obsolete.

Risk assessment should be drug specific.

Important considerations include:

• Maternal infection
• Gestational age
• Expected therapeutic benefit
• Alternative therapies
• Drug-specific fetal effects

Ribavirin remains particularly important because of its reproductive toxicity.

A blanket category-based approach should not replace contemporary drug-specific guidance.

Safeguarding

Rigid age cutoffs for assuming neglect, abuse, or intentional poisoning are outdated.

Assess pediatric exposures using:

• Developmental capability
• Access to medication
• Exposure circumstances
• Consistency of history
• Recurrent events
• Broader safeguarding concerns

Prognosis

Most minor antiviral exposures have favorable outcomes.

Important exceptions include:

• Severe amantadine cardiotoxicity
• Acyclovir/valacyclovir neurotoxicity with renal failure
• Persistent cidofovir-associated proximal tubular injury
• Severe foscarnet renal/electrolyte toxicity
• Profound ganciclovir-associated marrow suppression
• Clinically important ribavirin-associated hemolytic anemia

Outcome depends more on the specific antiviral and affected organ system than on the broad label “antiviral poisoning.”

Important Modernization of the Older Source

• These antivirals should not be treated as one toxicologic class.
• Valganciclovir belongs with ganciclovir in a modern discussion.
• Acyclovir/valacyclovir can cause crystal nephropathy plus neurotoxicity, especially with renal impairment.
• Hemodialysis can enhance acyclovir elimination in selected severe accumulation.
• Amantadine is no longer routinely used for influenza because of widespread resistance but remains relevant in neurologic practice.
• Amantadine toxicity includes CNS, antimuscarinic-like, and potentially severe cardiac effects.
• Renal impairment markedly increases amantadine toxicity.
• Physostigmine is not a routine amantadine antidote, particularly when conduction abnormalities or seizure risk exist.
• Conventional hemodialysis removes relatively little amantadine.
• Cidofovir → proximal tubular injury/Fanconi syndrome.
• Probenecid is principally preventive nephroprotection during cidofovir therapy, not a proven universal rescue antidote after overdose.
• Foscarnet → nephrotoxicity plus calcium, magnesium, potassium, and phosphate disturbances.
• Ionized calcium can be particularly informative during symptomatic foscarnet toxicity.
• Ganciclovir/valganciclovir → neutropenia, thrombocytopenia, anemia, with increased toxicity during renal impairment.
• Ribavirin → hemolytic anemia and important reproductive toxicity.
• The historical FDA pregnancy categories are obsolete.
• Ipecac and routine gastric lavage are obsolete.
• A fixed 4–6 hour observation period is inappropriate because several toxicities may be delayed.
• There is no universal antiviral antidote; management is agent-specific and complication-directed.

Key Points

• Acyclovir/valacyclovir → AKI/crystal nephropathy + neurotoxicity.
• Amantadine → delirium/seizures + potentially dangerous ventricular dysrhythmias.
• Cidofovir → proximal tubular injury/Fanconi syndrome.
• Foscarnet → AKI + major electrolyte disturbances, especially hypocalcemia and hypomagnesemia.
• Ganciclovir/valganciclovir → bone-marrow suppression.
• Ribavirin → hemolytic anemia.
• Renal dysfunction is a major amplifier of toxicity for several antiviral agents.
• Hemodialysis is useful for selected severe acyclovir or ganciclovir accumulation, but not as a universal antiviral treatment.
• There is no single specific antidote for this group.
• Treatment is primarily withdrawal of the offending drug, supportive care, correction of organ-specific complications, and appropriate renal dose adjustment.

Toxicology – Antiprotozoal Medications

Core Concept

This older grouping focuses on three very different drugs:

• Chloroquine
• Hydroxychloroquine
• Metronidazole

They should not be treated as a single toxicologic class.

The most important distinction is:

• Chloroquine/hydroxychloroquine overdose → potentially rapid, life-threatening cardiotoxicity
• Metronidazole overdose → usually GI and neurologic toxicity, generally much less acutely cardiotoxic

Chloroquine and hydroxychloroquine poisoning can deteriorate extremely quickly, with hypotension, conduction abnormalities, ventricular dysrhythmias, seizures, and cardiac arrest.

1. Chloroquine

Chloroquine is an antimalarial and antiprotozoal medication that also has important cardiac electrophysiologic effects.

In overdose it behaves partly as a potent membrane-stabilizing/sodium-channel–blocking toxin.

It can also interfere with other cardiac ion channels.

The result can be:

Rapid conduction slowing + myocardial depression + vasodilation + electrolyte disturbance → cardiovascular collapse

Chloroquine Has a Narrow Safety Margin

Chloroquine is unusual because relatively modest multiples of therapeutic exposure can cause severe poisoning.

Historical fixed gram-based toxicity thresholds should not be used as the sole basis for risk assessment, particularly in children.

Any credible significant chloroquine overdose should be treated as a medical emergency.

Rapid Onset

Serious chloroquine toxicity generally develops early.

Possible progression:

GI symptoms → dizziness/agitation → hypotension → QRS/QT abnormalities → ventricular dysrhythmia → seizure/coma → cardiac arrest

A patient can deteriorate rapidly despite appearing relatively well initially.

Cardiovascular Toxicity

Major manifestations include:

• Hypotension
• Tachycardia
• QRS widening
• QT prolongation
• AV/intraventricular conduction abnormalities
• Ventricular ectopy
• Ventricular tachyarrhythmias
• Severe myocardial depression
• Cardiac arrest

Continuous ECG and hemodynamic monitoring are essential in significant poisoning.

Hypokalemia – Key Feature

A characteristic feature of severe chloroquine poisoning is hypokalemia.

This is largely caused by an intracellular shift of potassium rather than necessarily reflecting true whole-body potassium depletion.

Severe poisoning may therefore produce:

• Low serum potassium
• Muscle weakness
• Increased electrical instability

Potassium Replacement – Important Caution

Hypokalemia should be monitored carefully, but overly aggressive potassium replacement can be dangerous.

As chloroquine toxicity resolves:

Intracellularly shifted K⁺ can move back extracellularly → rebound hyperkalemia

Therefore potassium correction should be carefully titrated with frequent reassessment.

Neurologic Toxicity

Severe chloroquine poisoning may cause:

• Headache
• Agitation
• Confusion
• Seizures
• CNS depression
• Coma

Seizures can worsen:

• Hypoxia
• Acidosis
• Cardiovascular instability

Rapid control is therefore important.

Respiratory Toxicity

Respiratory compromise may result from:

• CNS depression
• Seizures
• Severe shock
• Cardiac arrest

Early airway control may be necessary in severe poisoning, especially when cardiovascular deterioration is progressing.

2. Hydroxychloroquine

Hydroxychloroquine is closely related to chloroquine.

Although widely used for autoimmune diseases rather than protozoal infection in contemporary practice, its overdose syndrome resembles chloroquine toxicity.

Important acute effects include:

• Hypotension
• Hypokalemia
• QRS widening
• QT prolongation
• Ventricular dysrhythmias
• Seizures
• CNS depression
• Cardiovascular collapse

A significant hydroxychloroquine overdose should therefore be approached as a potentially severe cardiotoxic poisoning.

Chloroquine vs Hydroxychloroquine

Both drugs can produce rapid cardiovascular toxicity.

Chloroquine has the strongest historical evidence base for classic severe poisoning management, while hydroxychloroquine overdose is generally managed using similar toxicologic principles because of their pharmacologic similarities.

Chronic Retinal Toxicity

Both chloroquine and hydroxychloroquine can cause retinal injury during chronic therapy.

Features may include:

• Reduced visual acuity
• Paracentral or central visual-field defects
• Difficulty reading
• Altered color vision
• Progressive retinopathy

This is primarily a cumulative therapeutic toxicity, not the expected manifestation of acute overdose.

Hydroxychloroquine Retinopathy

Risk relates to factors such as:

• Daily exposure relative to body size
• Duration of therapy
• Cumulative exposure
• Renal dysfunction
• Concurrent retinal risk factors

Retinal injury may continue to progress after the drug has been stopped because of prolonged tissue retention.

Ophthalmologic Monitoring

Long-term hydroxychloroquine treatment requires appropriate retinal screening using modern ophthalmologic methods.

These may include:

• Automated visual-field testing
• Spectral-domain OCT
• Other specialized retinal tests when indicated

Routine acute overdose management does not depend on an immediate retinal examination unless visual symptoms or another indication exists.

Other Chronic Chloroquine/Hydroxychloroquine Toxicity

Long-term therapy can rarely cause:

• Skeletal myopathy
• Neuropathy
• Cardiomyopathy
• Conduction disease
• Hearing abnormalities
• Skin pigmentation changes

These should be distinguished from the rapid cardiovascular syndrome of acute overdose.

3. Metronidazole

Metronidazole is a nitroimidazole antimicrobial used against:

• Anaerobic bacteria
• Trichomonas
• Giardia
• Entamoeba and other susceptible organisms

Acute overdose is generally much less dangerous than chloroquine or hydroxychloroquine poisoning.

Acute Metronidazole Toxicity

Common effects include:

• Nausea
• Vomiting
• Abdominal discomfort
• Metallic taste
• Headache
• Dizziness
• Drowsiness
• Ataxia

Most isolated acute exposures are managed supportively.

Metronidazole Neurotoxicity

Prolonged or excessive exposure can produce clinically important neurologic toxicity.

Manifestations include:

• Ataxia
• Dysarthria
• Confusion
• Encephalopathy
• Peripheral neuropathy
• Seizures

Metronidazole-Induced Encephalopathy

Characteristic findings may include:

• Gait instability
• Dysarthria
• Altered mental status
• Cerebellar dysfunction

MRI can show characteristic abnormalities, including lesions involving the dentate nuclei and other CNS structures.

Symptoms frequently improve after discontinuation, although recovery can take time.

Peripheral Neuropathy

Prolonged metronidazole exposure can cause:

• Numbness
• Tingling
• Burning sensations
• Distal sensory impairment

Risk is more closely related to cumulative exposure than to a single modest ingestion.

Metronidazole and Alcohol

Older literature commonly states that metronidazole reliably causes a classic disulfiram-like reaction with ethanol.

Modern evidence is less convincing.

Although avoidance of alcohol during treatment is still commonly recommended in product guidance, the mechanism and consistency of a true disulfiram-like interaction are uncertain.

Therefore, flushing or vomiting after alcohol plus metronidazole should not automatically be assumed to prove an acetaldehyde-mediated disulfiram reaction.

Metronidazole Drug Interactions

Important interactions include:

Warfarin

Metronidazole can increase anticoagulant effect, potentially raising INR and bleeding risk.

Lithium

Lithium concentrations may increase in some patients, particularly when renal function changes.

Enzyme-inducing antiseizure medications

Some can increase metronidazole metabolism and reduce exposure.

A severe or atypical presentation should therefore include a complete medication review.

Dark Urine

Metronidazole can occasionally cause dark or reddish-brown urine due to metabolites.

This finding alone does not necessarily indicate hematuria or renal failure.

Hematologic Effects

Rare effects include:

• Leukopenia
• Neutropenia
• Thrombocytopenia

These are more relevant to therapeutic or prolonged exposure than uncomplicated acute overdose.

Hepatic Considerations

Metronidazole is metabolized hepatically.

Significant hepatic dysfunction can reduce clearance and increase systemic exposure.

Rare clinically important hepatotoxicity can also occur.

Diagnosis

The first priority is determining the exact drug.

For chloroquine/hydroxychloroquine

Assess immediately:

• Amount and timing
• Symptoms
• Blood pressure
• ECG
• Potassium
• Glucose
• Other electrolytes
• Acid–base status when severely ill
• Coingestants

For metronidazole

Assess:

• Acute vs cumulative exposure
• Neurologic findings
• Hepatic function when relevant
• Interacting medications
• Coingestants

ECG in Chloroquine/Hydroxychloroquine Poisoning

Obtain an ECG early and monitor serially.

Assess:

• Heart rate
• Rhythm
• PR interval
• QRS duration
• QT/QTc
• Ventricular ectopy

Progressive conduction abnormalities may precede cardiovascular collapse.

Laboratory Evaluation

For significant chloroquine/hydroxychloroquine exposure, consider:

• Potassium
• Magnesium
• Calcium
• Sodium
• Glucose
• Renal function
• Blood gas/lactate in severe poisoning

Frequent potassium reassessment may be required because concentrations can change rapidly during recovery.

Drug Concentrations

Routine serum chloroquine, hydroxychloroquine, or metronidazole concentrations are generally not sufficiently available or actionable to guide acute emergency management.

Treatment should be driven by:

• Clinical severity
• ECG
• Hemodynamics
• Electrolytes

Management of Chloroquine/Hydroxychloroquine Poisoning

Priorities are:

Airway → continuous ECG → circulation → potassium/electrolytes → seizures → aggressive treatment of shock and dysrhythmia

Early toxicology/poison-center consultation is strongly appropriate for any significant exposure.

Airway Management

Severe chloroquine poisoning may deteriorate abruptly.

Early controlled airway management should be considered when there is:

• Severe CNS depression
• Recurrent seizures
• Progressive shock
• Respiratory failure

Peri-intubation cardiovascular collapse is a major concern in severely poisoned patients, so resuscitation must proceed concurrently.

Epinephrine

Epinephrine has an important role in severe chloroquine poisoning with hypotension and myocardial depression.

It can improve:

• Blood pressure
• Cardiac output
• Contractility

Vasopressor therapy should be titrated to clinical response under intensive monitoring rather than according to rigid historical dose targets.

High-Dose Diazepam – Important Historical Therapy

Older literature describes high-dose diazepam as a central treatment for severe chloroquine poisoning.

Modern interpretation is more nuanced.

Benzodiazepines are clearly appropriate for:

• Seizures
• Agitation
• Sedation when required

Historical observational evidence suggested benefit from high-dose diazepam combined with epinephrine in severe chloroquine poisoning, but the evidence is limited and does not establish diazepam as a universal antidote.

Very high-dose diazepam regimens should therefore be undertaken only with specialist toxicology guidance and intensive airway/hemodynamic monitoring.

Sodium Bicarbonate

Because chloroquine can produce sodium-channel blockade and QRS widening, sodium bicarbonate may be considered in selected severe conduction toxicity.

However, this requires caution because alkalemia can further reduce serum potassium.

Treatment should therefore be guided by:

• ECG
• Potassium
• Acid–base status
• Hemodynamics
• Toxicology expertise

It is not a routine treatment for every chloroquine ingestion.

Ventricular Dysrhythmias

Priorities include:

• Optimize oxygenation
• Correct severe acidemia
• Carefully manage potassium
• Correct magnesium when indicated
• Treat shock
• Address sodium-channel blockade when appropriate

Antiarrhythmic selection requires caution because some agents can worsen conduction or QT abnormalities.

Seizures

Benzodiazepines are first-line.

Persistent seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic therapy

Correct:

• Hypoglycemia
• Hypoxia
• Electrolyte abnormalities
• Acid–base disturbance

GI Decontamination

Do not induce vomiting.

Ipecac is obsolete.

Routine gastric lavage is not standard management.

Because chloroquine/hydroxychloroquine can become life-threatening rapidly, airway and cardiovascular stabilization take priority over GI decontamination.

Activated charcoal may be considered after a clinically important recent ingestion when:

• The airway is protected
• Aspiration risk is acceptable
• Administration will not delay resuscitation

Metronidazole Management

Most acute metronidazole overdoses require:

• Supportive care
• Fluids if clinically dehydrated
• Antiemetic therapy when appropriate
• Neurologic observation
• Seizure treatment if required

For chronic neurotoxicity:

Stop metronidazole and provide supportive neurologic care.

There is no specific antidote.

Enhanced Elimination

Routine enhanced elimination is not recommended for chloroquine, hydroxychloroquine, or metronidazole poisoning.

Chloroquine and hydroxychloroquine have extensive tissue distribution, making conventional dialysis ineffective for meaningful toxin removal.

Extracorporeal life support such as VA-ECMO may be considered as circulatory rescue in selected refractory cardiogenic/cardiotoxic collapse, but this supports the patient while toxicity resolves—it does not meaningfully eliminate the drug.

Observation

A universal fixed observation period is inappropriate.

Chloroquine/hydroxychloroquine

Significant exposures require monitored medical evaluation because severe toxicity can develop rapidly.

Disposition depends on:

• Exposure magnitude
• Symptoms
• ECG
• Potassium
• Blood pressure
• Mental status
• Clinical trajectory

Metronidazole

Minor asymptomatic exposures generally require much less intensive monitoring.

Prolonged exposure requires assessment for delayed neurologic toxicity.

Admission

Hospitalization is appropriate for chloroquine/hydroxychloroquine poisoning with:

• Significant or uncertain overdose
• Hypotension
• Hypokalemia
• QRS/QT abnormality
• Ventricular ectopy/dysrhythmia
• Seizure
• Altered mental status
• Respiratory compromise

ICU care is appropriate for clinically significant cardiotoxicity.

For metronidazole, admission may be appropriate for:

• Persistent encephalopathy
• Severe ataxia
• Seizures
• Significant dehydration
• Serious coingestion or interaction

Pregnancy and Breastfeeding

Historical FDA pregnancy letter categories are obsolete.

The statement that metronidazole should simply be avoided throughout pregnancy is also outdated.

Modern decisions consider:

• Drug
• Infection
• Gestational age
• Maternal benefit
• Fetal risk
• Available alternatives

Chloroquine and hydroxychloroquine have established therapeutic uses during pregnancy in appropriate clinical circumstances.

Breastfeeding recommendations should similarly be drug- and indication-specific.

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional poisoning are inappropriate.

Evaluate pediatric exposures according to:

• Developmental capability
• Medication accessibility
• Circumstances
• Consistency of history
• Recurrent events
• Broader safeguarding concerns

Prognosis

Chloroquine/Hydroxychloroquine

Outcome depends heavily on the severity of early cardiovascular toxicity.

Poor prognostic features include:

• Severe hypotension
• Marked conduction abnormalities
• Ventricular dysrhythmias
• Severe hypokalemia
• Seizures
• Cardiac arrest

Patients who survive the acute cardiotoxic phase may recover substantially, although hypoxic injury can cause persistent deficits.

Metronidazole

Most acute exposures have a favorable prognosis.

Chronic neurotoxicity often improves after discontinuation, although peripheral neuropathy may recover slowly or occasionally persist.

Important Modernization of the Older Source

• Chloroquine and hydroxychloroquine overdose should be separated toxicologically from metronidazole.
• Chloroquine/hydroxychloroquine poisoning is a rapidly developing cardiotoxic emergency.
• Sodium-channel blockade contributes to QRS widening and ventricular dysrhythmias.
• Hypokalemia is a characteristic marker of severe chloroquine toxicity, largely reflecting intracellular redistribution.
• Potassium replacement requires caution because rebound hyperkalemia can occur during recovery.
• Significant hydroxychloroquine overdose can produce a syndrome similar to chloroquine poisoning.
• Chronic retinal toxicity should not be confused with the acute overdose syndrome.
• Epinephrine remains an important vasopressor/inotropic therapy in severe chloroquine poisoning.
• High-dose diazepam is historically associated with severe chloroquine treatment, but evidence is limited; it should not be described as a universally proven antidote.
• Sodium bicarbonate may have a role for selected significant sodium-channel blockade but requires careful potassium and acid–base monitoring.
• Dialysis is ineffective for meaningful chloroquine/hydroxychloroquine elimination.
• VA-ECMO can be considered as rescue support for refractory cardiovascular collapse; it is not an elimination technique.
• Metronidazole overdose is usually much less severe.
• Prolonged metronidazole exposure can cause encephalopathy, cerebellar dysfunction, and peripheral neuropathy.
• The classic metronidazole–ethanol “disulfiram reaction” is less firmly established than older teaching suggested.
• Metronidazole can interact importantly with warfarin and lithium.
• Ipecac is obsolete and routine gastric lavage is not standard.
• Fixed 2-, 4-, or 8-hour discharge rules are too rigid.
• Historical FDA pregnancy categories and blanket metronidazole pregnancy avoidance are outdated.

Key Points

• Chloroquine/hydroxychloroquine → rapid, potentially fatal cardiotoxicity.
• QRS widening + hypotension + hypokalemia are particularly concerning in chloroquine poisoning.
• Severe cases can progress quickly to ventricular dysrhythmia, seizure, shock, and cardiac arrest.
• Epinephrine has an important role in severe chloroquine-associated cardiovascular collapse.
• Benzodiazepines treat seizures; historical high-dose diazepam therapy requires specialist guidance.
• Potassium must be corrected cautiously because rebound hyperkalemia can occur.
• Metronidazole → GI symptoms and, with substantial/cumulative exposure, neurotoxicity.
• Metronidazole-induced encephalopathy often features cerebellar dysfunction and may have characteristic MRI abnormalities.
• There is no universal specific antidote for these agents.
• Significant chloroquine or hydroxychloroquine exposure warrants rapid monitored evaluation and early toxicology/poison-center involvement.

Toxicology – Benzimidazole Antiparasitic Drugs

Core Concept

This older “antiparasitic drugs” entry mainly describes the benzimidazole anthelmintics:

• Albendazole
• Mebendazole
• Thiabendazole

These drugs are used against various helminth infections. Thiabendazole is now much less commonly used systemically because newer agents generally have better tolerability.

Acute isolated overdose is usually mild and self-limited. More important toxicity tends to occur during prolonged or high-dose therapy and includes:

• GI symptoms
• Hepatotoxicity
• Rare bone-marrow suppression
• Hypersensitivity reactions
• Neurologic symptoms

There is no specific antidote.

Mechanism

Benzimidazoles bind parasite β-tubulin and disrupt microtubule formation.

This interferes with:

• Glucose uptake
• Intracellular transport
• Secretory processes
• Energy production
• Parasite survival

The older description that all these drugs are simply poorly absorbed is too broad.

Mebendazole

Generally has limited systemic bioavailability.

Albendazole

The parent drug is poorly absorbed but is rapidly converted to albendazole sulfoxide, an active systemically available metabolite.

Systemic exposure is important when treating tissue parasites such as neurocysticercosis or echinococcosis.

Thiabendazole

Is considerably better absorbed and therefore produces more systemic adverse effects.

Acute Overdose

Most acute exposures produce:

• Nausea
• Vomiting
• Abdominal discomfort
• Diarrhea
• Headache
• Dizziness
• Drowsiness

Serious acute poisoning is uncommon.

Thiabendazole historically produces more adverse effects than albendazole or mebendazole.

1. Gastrointestinal Toxicity

GI symptoms are the most common adverse effects.

Possible manifestations include:

• Anorexia
• Nausea
• Vomiting
• Abdominal pain
• Diarrhea

These effects are usually managed supportively.

Persistent vomiting can occasionally result in:

• Dehydration
• Electrolyte abnormalities
• Orthostatic symptoms

2. Hepatotoxicity

Albendazole and mebendazole can cause elevations in liver enzymes, particularly during prolonged systemic therapy.

Rare clinically important liver injury may occur.

Possible manifestations include:

• Nausea
• Fatigue
• Right-upper-quadrant discomfort
• Elevated AST/ALT
• Jaundice

Risk is more relevant during repeated or prolonged therapy than after a small accidental ingestion.

Monitoring During Prolonged Therapy

When albendazole is used for prolonged systemic treatment, monitoring commonly includes:

• Liver function tests
• CBC

Significant abnormalities may require interruption or reassessment of therapy.

A normal initial liver panel after an acute exposure does not predict all delayed adverse reactions from prolonged treatment.

3. Bone-Marrow Suppression

Rare hematologic toxicity has been reported with systemic benzimidazole therapy, particularly prolonged albendazole treatment.

Possible abnormalities include:

• Leukopenia
• Neutropenia
• Thrombocytopenia
• Pancytopenia

Severe marrow toxicity is uncommon but potentially serious.

Patients receiving prolonged treatment may therefore require serial CBC monitoring.

4. Neurologic Effects

Possible CNS effects include:

• Headache
• Dizziness
• Drowsiness
• Confusion
• Rare hallucinations

Seizures have occasionally been reported, but they are not the expected manifestation of uncomplicated benzimidazole overdose.

If seizures occur, consider:

• Large or mixed exposure
• Metabolic abnormalities
• CNS infection
• Underlying neurologic disease
• Treatment of a CNS parasitic infection
• Other medications

Neurocysticercosis – Important Clinical Distinction

Neurologic deterioration after albendazole treatment for neurocysticercosis does not necessarily represent direct drug poisoning.

Destruction of intracranial parasites can provoke an inflammatory response, potentially worsening:

• Headache
• Cerebral edema
• Seizures
• Focal neurologic abnormalities

This is a treatment-associated inflammatory phenomenon rather than conventional albendazole overdose.

Seizure Management

For toxicologic seizures:

Benzodiazepines are first-line.

Persistent seizures may require additional benzodiazepines, phenobarbital, or appropriate anesthetic management.

Also correct:

• Hypoglycemia
• Hypoxia
• Electrolyte abnormalities
• Acid–base disturbances

5. Hypersensitivity

Benzimidazoles can rarely cause:

• Rash
• Urticaria
• Pruritus
• Angioedema
• Severe cutaneous reactions

SJS/TEN has been reported rarely.

A severe mucocutaneous eruption requires immediate discontinuation and urgent medical evaluation.

6. Thiabendazole

Thiabendazole is considerably more likely than albendazole or mebendazole to produce systemic adverse effects.

Reported effects include:

• Nausea/vomiting
• Dizziness
• Drowsiness
• Headache
• Visual disturbances
• Tinnitus
• Hypotension
• Neuropsychiatric symptoms
• Hepatic dysfunction

Its unfavorable adverse-effect profile is one reason systemic thiabendazole has largely been replaced by better-tolerated therapies for many infections.

7. Drug Interactions

Mebendazole

Cimetidine can inhibit metabolism and increase systemic mebendazole exposure, although the clinical importance depends on the treatment setting.

A particularly important modern interaction is:

Mebendazole + metronidazole

This combination has been associated with an increased risk of severe cutaneous adverse reactions such as SJS/TEN and is generally avoided.

Thiabendazole

Thiabendazole can inhibit the metabolism of theophylline.

Theophylline accumulation can produce:

• Nausea/vomiting
• Tremor
• Tachycardia
• Agitation
• Seizures
• Dysrhythmias

A severe presentation in a patient taking both drugs should therefore raise concern for secondary theophylline toxicity.

Albendazole

Albendazole is converted to active albendazole sulfoxide.

Some medications can alter concentrations of its active metabolite.

The older source contains spelling errors such as “abendaxole” and “dexamethadone”; these refer to albendazole and dexamethasone.

Drug interactions are usually more relevant during systemic treatment than during a single accidental exposure.

8. Renal Effects

The older source lists hemolytic-uremic syndrome as though it were a characteristic class effect.

This is not a defining toxicity of modern benzimidazole poisoning.

If AKI develops, evaluate for alternative or contributing causes such as:

• Dehydration
• Sepsis
• Hemolysis
• Other nephrotoxins
• Underlying illness

Routine renal failure is not expected after an uncomplicated benzimidazole overdose.

9. Pregnancy

The historical FDA pregnancy letter categories are obsolete.

Pregnancy recommendations are now agent- and indication-specific.

Albendazole and mebendazole may be used in selected circumstances when treatment benefits justify exposure, including in public-health deworming programs under appropriate guidance.

Therefore, the older statement that all these agents are simply “relatively contraindicated” throughout pregnancy is too broad.

Consider:

• Specific parasite
• Severity of infection
• Gestational stage
• Expected treatment benefit
• Available alternatives

Breastfeeding

Breastfeeding recommendations should also be drug specific.

Albendazole and mebendazole generally produce relatively limited infant exposure with commonly used regimens, but the indication and treatment duration should still be considered.

A blanket class-wide prohibition is not appropriate.

Diagnosis

Determine:

• Exact antiparasitic
• Amount
• Timing
• Single vs repeated exposure
• Treatment duration
• Underlying parasitic infection
• Liver disease
• Coingestants
• Interacting medications

When neurologic deterioration occurs during treatment of a CNS parasite, distinguish direct drug toxicity from inflammation caused by parasite destruction.

Laboratory Evaluation

No laboratory tests may be required after a small, asymptomatic acute ingestion.

For significant symptoms or prolonged/high-dose therapy, consider:

• CBC
• Electrolytes
• Glucose
• BUN/creatinine
• Liver function tests

Additional testing should be directed by the presentation.

Drug Concentrations

Routine serum albendazole, mebendazole, or thiabendazole concentrations have no established role in managing most acute overdoses.

Clinical findings and organ-function testing are more useful.

ECG

Routine continuous cardiac monitoring is unnecessary after every uncomplicated exposure.

Obtain an ECG when there is:

• Significant hypotension
• Palpitations
• Syncope
• Major systemic toxicity
• Suspected theophylline interaction
• Relevant coingestion

This replaces the older blanket recommendation for cardiac monitoring after poisoning.

Initial Management

General priorities are:

Airway/breathing → circulation → identify exact drug → assess neurologic status → evaluate GI losses → consider liver/marrow toxicity when relevant → identify interactions/coingestants

Most acute exposures require only supportive treatment.

GI Decontamination

Do not induce vomiting.

Ipecac is obsolete.

Routine gastric lavage is also obsolete.

Activated charcoal may occasionally be considered after a substantial recent ingestion when:

• The exposure is clinically important
• The drug is adsorbable
• The airway is safe
• Aspiration risk is acceptable

Most minor accidental benzimidazole ingestions do not require decontamination.

Hypotension

Significant hypotension is unusual.

If present, consider:

• Dehydration from vomiting
• Hypersensitivity/anaphylaxis
• Thiabendazole toxicity
• Coingestants
• Other illness

Treat clinically significant volume depletion with appropriate isotonic fluid.

Persistent shock should be managed according to its physiology rather than with a rigid historical vasopressor sequence.

Anaphylaxis

For true anaphylaxis:

IM epinephrine is first-line therapy.

Airway, oxygenation, and circulatory support should be provided as required.

Antihistamines are adjuncts and must not delay epinephrine.

Enhanced Elimination

There is no established routine role for:

• Hemodialysis
• Hemoperfusion
• Multiple-dose activated charcoal

in uncomplicated benzimidazole overdose.

Renal replacement therapy may still be required for conventional indications if unrelated severe organ failure develops.

No Specific Antidote

There is no specific antidote for:

• Albendazole
• Mebendazole
• Thiabendazole

Treatment consists mainly of:

Stopping exposure + supportive care + managing complications

Observation

The historical fixed 8-hour observation rule is unnecessarily rigid.

Observation should instead depend on:

• Exact drug
• Amount
• Symptoms
• Coingestants
• Interactions
• Liver function when relevant
• Clinical trajectory

Most acute effects develop relatively early, but delayed marrow or hepatic toxicity associated with prolonged therapy cannot be excluded by a short ED observation period.

Admission

Hospitalization may be appropriate for:

• Persistent altered mental status
• Seizures
• Significant hypotension
• Severe vomiting/dehydration
• Clinically important hepatic injury
• Significant cytopenias
• Severe hypersensitivity
• SJS/TEN
• Serious interacting-drug toxicity

ICU care is reserved for severe neurologic, respiratory, or hemodynamic complications.

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional poisoning are outdated.

Pediatric exposures should instead be assessed according to:

• Developmental capability
• Medication accessibility
• Circumstances of exposure
• Consistency of history
• Recurrent unexplained events
• Broader safeguarding concerns

Prognosis

Most isolated acute benzimidazole exposures have an excellent prognosis.

Potentially important complications are more likely with:

• Prolonged systemic treatment
• Significant hepatic dysfunction
• Drug interactions
• Rare severe hypersensitivity
• Significant marrow suppression

Most uncomplicated acute symptoms resolve with supportive care.

Important Modernization of the Older Source

• This entry specifically concerns benzimidazole anthelmintics, not antiparasitic drugs as a whole.
• Albendazole, mebendazole, and thiabendazole disrupt parasite microtubules.
• The statement that all are poorly absorbed is inaccurate: thiabendazole is systemically absorbed, while albendazole forms an active systemic metabolite.
• Acute overdose is generally mild and GI-predominant.
• Thiabendazole has more systemic adverse effects and is now much less commonly used.
• Prolonged albendazole therapy can cause hepatotoxicity and bone-marrow suppression.
• Neurologic worsening during neurocysticercosis treatment may result from inflammation around dying parasites rather than direct albendazole poisoning.
• Mebendazole plus metronidazole is an important interaction because of severe cutaneous reaction risk.
• Thiabendazole can increase theophylline exposure.
• Hemolytic-uremic syndrome is not a defining class toxicity.
• Serum benzimidazole concentrations generally do not guide acute toxicology management.
• Routine cardiac monitoring is unnecessary after every minor exposure.
• Ipecac and routine gastric lavage are obsolete.
• There is no specific antidote or routine role for extracorporeal removal.
• A fixed 8-hour observation period is unnecessary.
• Historical FDA pregnancy categories and blanket pregnancy contraindications are outdated.
• Pediatric safeguarding should not use rigid age cutoffs.

Key Points

• Albendazole, mebendazole, and thiabendazole are benzimidazole anthelmintics.
• Acute overdose is usually mild, with GI symptoms, headache, or dizziness.
• Thiabendazole produces the most systemic adverse effects of these older agents.
• Prolonged albendazole/mebendazole exposure can rarely cause hepatotoxicity and marrow suppression.
• Albendazole’s active metabolite achieves systemic exposure and is important in treatment of tissue parasites.
• CNS symptoms during neurocysticercosis treatment may reflect an inflammatory response to parasite death, not poisoning.
• Mebendazole + metronidazole should be avoided because of severe cutaneous reaction risk.
• Thiabendazole can increase theophylline concentrations.
• There is no specific antidote.
• Management of acute overdose is predominantly supportive and symptom-directed.

Toxicology – Antineoplastic Medications

Core Concept

Antineoplastic drugs comprise many pharmacologically unrelated agents used to treat malignancy. Some, particularly methotrexate, are also used for nonmalignant diseases.

Unlike many medication ingestions, antineoplastic overdose is potentially serious because toxicity may be:

• Delayed
• Multisystem
• Prolonged
• Dose- and route-dependent
• Associated with profound myelosuppression
• Complicated by renal, hepatic, cardiac, neurologic, or pulmonary injury

A patient can initially appear well and subsequently develop severe toxicity days or even weeks later.

Management therefore requires identification of the exact drug, route, dose, timing, and treatment protocol, usually with early toxicology and oncology involvement.

Major Antineoplastic Classes

Important groups include:

Antimetabolites

• Methotrexate
• 5-fluorouracil (5-FU)
• Cytarabine

Alkylating agents

• Cyclophosphamide
• Ifosfamide
• Melphalan
• Chlorambucil
• Mechlorethamine
• Carmustine
• Lomustine

Platinum compounds

• Cisplatin
• Carboplatin
• Oxaliplatin

Anthracyclines

• Doxorubicin
• Daunorubicin

Vinca alkaloids

• Vincristine
• Vinblastine

Topoisomerase inhibitors

• Etoposide

Microtubule-stabilizing agents

• Paclitaxel and related taxanes

Other cytotoxic agents

• Bleomycin
• Dactinomycin
• Mitomycin
• Asparaginase

Modern oncology also includes targeted therapies, monoclonal antibodies, immune checkpoint inhibitors, antibody-drug conjugates, and other agents whose toxicity differs substantially from traditional cytotoxic chemotherapy.

Why Antineoplastic Toxicity Is Different

Many cytotoxic drugs preferentially injure rapidly dividing cells.

Consequently, major target tissues include:

• Bone marrow
• GI epithelium
• Oral mucosa
• Hair follicles
• Reproductive tissues

Individual drugs additionally have characteristic organ toxicities.

A useful framework is:

Exposure → early GI/mucosal toxicity → delayed marrow suppression ± agent-specific organ injury

Delayed Toxicity

A critical toxicology principle is that absence of early symptoms does not exclude severe poisoning.

Delayed complications may include:

• Neutropenia
• Thrombocytopenia
• Anemia
• Mucositis
• Infection
• Sepsis
• Bleeding
• Organ failure

Some agents, particularly nitrosoureas, can cause marrow suppression substantially later than the classic first 1–2 weeks.

1. Methotrexate

Methotrexate inhibits dihydrofolate reductase, impairing tetrahydrofolate production and nucleotide synthesis.

Major toxicities include:

• Mucositis
• Myelosuppression
• GI injury
• Hepatotoxicity
• Nephrotoxicity
• Neurotoxicity
• Pulmonary toxicity

High-dose therapy is particularly dangerous when renal elimination becomes impaired.

Methotrexate Nephrotoxicity

Methotrexate and its metabolites may precipitate within renal tubules.

This can produce:

Crystal nephropathy → reduced clearance → rising methotrexate concentration → further toxicity

This creates a potentially dangerous positive-feedback cycle.

Risk increases with:

• High-dose therapy
• Dehydration
• Acidic urine
• Preexisting renal impairment
• Interacting medications

Methotrexate Drug Interactions

Medications that interfere with renal clearance can increase toxicity.

Examples may include:

• NSAIDs
• Certain antibiotics
• Proton-pump inhibitors in some high-dose settings
• Other nephrotoxic or renally competing medications

Medication review is therefore essential when methotrexate elimination is delayed.

Methotrexate – Leucovorin Rescue

Leucovorin (folinic acid) bypasses the folate pathway blocked by methotrexate and is a central rescue therapy for clinically important systemic methotrexate toxicity.

The amount and duration of leucovorin depend on:

• Methotrexate concentration
• Time since administration
• Renal function
• Evidence of delayed elimination
• Clinical toxicity

Historical fixed concentration cutoffs should not substitute for the appropriate treatment protocol or nomogram.

Glucarpidase

A major modern addition is glucarpidase.

It rapidly metabolizes circulating methotrexate through a pathway independent of renal clearance.

It may be indicated in selected patients with:

High-dose methotrexate + delayed elimination + significant renal dysfunction

Leucovorin therapy remains important, but its timing relative to glucarpidase matters and should follow specialist protocols.

Methotrexate Hydration and Urinary Alkalinization

High-dose methotrexate toxicity is managed with carefully controlled:

• IV hydration
• Urinary alkalinization
• Serial methotrexate concentrations
• Serial renal function
• Leucovorin rescue

The aim is to improve methotrexate solubility and renal elimination.

Exact fluid and bicarbonate regimens are protocol-specific rather than universal overdose formulas.

Methotrexate Routes Matter

Toxicity differs markedly between:

• Single acute oral exposure
• Repeated low-dose dosing errors
• High-dose IV chemotherapy
• Intrathecal exposure

A particularly important modern problem is accidental daily instead of weekly methotrexate dosing in patients prescribed low-dose therapy.

Repeated dosing errors can cause severe:

• Mucositis
• Pancytopenia
• Infection
• Bleeding
• Renal/hepatic injury

Intrathecal Methotrexate

Excessive intrathecal exposure can cause severe neurotoxicity, including:

• Headache
• Meningeal irritation
• Encephalopathy
• Seizures
• Motor deficits
• Leukoencephalopathy

This is a specialized emergency requiring immediate consultation with oncology, toxicology, neurology/neurosurgery, and other appropriate specialists.

Historical invasive CSF-exchange procedures should not be treated as routine bedside instructions.

2. 5-Fluorouracil – 5-FU

5-FU interferes with pyrimidine metabolism, particularly through inhibition of thymidylate synthase, while metabolites can also become incorporated into RNA and DNA.

Major toxicities include:

• Severe mucositis
• Diarrhea
• Myelosuppression
• Neurotoxicity
• Cardiotoxicity

5-FU Cardiotoxicity

5-FU can produce:

• Coronary vasospasm
• Chest pain
• Myocardial ischemia
• Dysrhythmia
• Cardiomyopathy
• Rare cardiogenic shock

Cardiac symptoms during infusion require prompt evaluation and cessation of the offending therapy.

5-FU and DPD Deficiency

A major modern concept is dihydropyrimidine dehydrogenase (DPD) deficiency.

DPD is crucial for fluoropyrimidine metabolism.

Reduced DPD activity can result in unexpectedly severe toxicity even with standard treatment.

Possible manifestations include:

• Profound diarrhea
• Mucositis
• Neutropenia
• Encephalopathy
• Multiorgan toxicity

Uridine Triacetate

Another major modernization is uridine triacetate, a specific emergency antidotal therapy for severe fluoropyrimidine toxicity.

It is used for selected:

• 5-FU overdoses
• Capecitabine overdoses
• Early severe/life-threatening fluoropyrimidine toxicity

Benefit is highly time dependent, so suspected serious fluoropyrimidine overdose warrants immediate specialist/poison-center consultation.

The historical suggestion that allopurinol prevents 5-FU overdose-related marrow suppression is not modern standard antidotal management.

3. Cytarabine

Cytarabine is a cytidine analog that inhibits DNA synthesis.

High systemic exposure can cause:

• Myelosuppression
• Mucositis
• Hepatic dysfunction
• Neurotoxicity

A characteristic complication of high-dose therapy is cerebellar toxicity.

Cytarabine Neurotoxicity

Possible findings include:

• Dysarthria
• Nystagmus
• Ataxia
• Dysmetria
• Confusion
• Encephalopathy

Risk increases with:

• Older age
• Renal dysfunction
• High-dose therapy

Serial neurologic examination is therefore important during high-dose treatment.

4. Cisplatin and Carboplatin

Platinum agents produce DNA cross-linking.

Cisplatin

Particularly associated with:

• Nephrotoxicity
• Ototoxicity
• Peripheral neuropathy
• Severe nausea/vomiting
• Electrolyte wasting

Carboplatin

More prominently associated with:

• Myelosuppression, especially thrombocytopenia

while generally being less nephrotoxic than cisplatin.

Cisplatin Electrolyte Toxicity

Renal tubular injury can produce:

• Hypomagnesemia
• Hypokalemia
• Hypocalcemia
• Other electrolyte abnormalities

Monitor:

• Creatinine
• Magnesium
• Potassium
• Calcium

Ototoxicity may manifest as tinnitus or high-frequency sensorineural hearing loss.

5. Cyclophosphamide and Ifosfamide

These alkylating agents generate toxic metabolites capable of injuring the urinary tract.

A classic complication is:

Hemorrhagic cystitis

Manifestations include:

• Dysuria
• Hematuria
• Bladder irritation

Mesna

Mesna binds urotoxic metabolites within the urinary tract and is used to prevent hemorrhagic cystitis associated particularly with ifosfamide and high-risk cyclophosphamide regimens.

Adequate hydration is also important.

This is more specific and clinically useful than relying on extremely high fixed fluid volumes from older toxicology references.

Ifosfamide Encephalopathy

Ifosfamide can cause:

• Confusion
• Somnolence
• Hallucinations
• Agitation
• Seizures
• Coma

Renal tubular dysfunction and metabolic abnormalities can also occur.

Selected severe cases of ifosfamide encephalopathy may be treated with methylene blue, although evidence is limited and specialist guidance is appropriate.

Cyclophosphamide Cardiotoxicity

High systemic exposure can cause:

• Myocardial injury
• Arrhythmia
• Heart failure
• Hemorrhagic myocarditis in severe cases

This is primarily associated with intensive treatment regimens rather than ordinary low-dose exposure.

6. Anthracyclines – Doxorubicin and Daunorubicin

Anthracyclines interfere with topoisomerase II, DNA function, and oxidative cellular pathways.

Important toxicities include:

• Myelosuppression
• Mucositis
• Cardiotoxicity
• Severe tissue injury after extravasation

Anthracycline Cardiotoxicity

Cardiac toxicity may be:

Acute

• ECG abnormalities
• Dysrhythmia
• Myopericarditis
• Transient ventricular dysfunction

Chronic

• Progressive cardiomyopathy
• Reduced ejection fraction
• Heart failure

Chronic risk generally rises with cumulative exposure but cannot be represented by a single universal dose cutoff because risk depends on the specific anthracycline and patient factors.

Dexrazoxane

Dexrazoxane can reduce anthracycline-related cardiac injury in selected treatment settings.

It also has an important modern role as an antidotal treatment for anthracycline extravasation.

Its use is indication- and timing-specific and should follow oncology/extravasation protocols.

7. Vinca Alkaloids

Vincristine

Toxicity is predominantly neurologic.

Possible manifestations include:

• Peripheral neuropathy
• Paresthesias
• Weakness
• Reduced reflexes
• Autonomic dysfunction
• Ileus
• Cranial neuropathies
• SIADH
• Severe neurotoxicity after excessive exposure

Vinblastine

Produces relatively more:

• Myelosuppression

although neurologic toxicity can also occur.

Vincristine – Intrathecal Exposure

Intrathecal vincristine is a catastrophic medical error and can be fatal.

Vincristine must never be administered intrathecally.

This requires immediate specialist emergency management.

Older descriptions of specific CSF-perfusion procedures should not be treated as a standard or universally effective antidote.

Prevention through safe chemotherapy systems is critical.

Vincristine Interactions

Vincristine neurotoxicity can be substantially increased by medications that impair its metabolism.

Clinically important interactions include some strong CYP3A inhibitors, particularly certain azole antifungals.

Medication reconciliation is therefore essential.

8. Etoposide

Etoposide inhibits topoisomerase II.

Major adverse effects include:

• Myelosuppression
• Nausea/vomiting
• Mucositis
• Hepatic injury at high exposure
• Hypersensitivity

Rapid IV administration can produce hypotension.

9. Paclitaxel

Paclitaxel stabilizes microtubules and prevents normal mitotic function.

Important adverse effects include:

• Neutropenia
• Peripheral neuropathy
• Hypersensitivity reactions
• Myalgias/arthralgias
• Cardiac conduction abnormalities in selected patients
• Mucositis

Acute overdose can produce severe marrow and neurologic toxicity.

10. Bleomycin

Bleomycin causes DNA strand injury.

Its characteristic dose-limiting organ toxicity is:

Pulmonary injury

Possible manifestations include:

• Dry cough
• Dyspnea
• Interstitial pneumonitis
• Pulmonary fibrosis

Bleomycin and Oxygen – Important Nuance

Older teaching sometimes implied that oxygen should simply be avoided in anyone previously exposed to bleomycin.

That is too absolute.

Hypoxemia must be treated.

However, unnecessary prolonged exposure to excessive inspired oxygen should be avoided when lower concentrations adequately maintain oxygenation, particularly in patients with established bleomycin lung injury.

11. Asparaginase

Asparaginase reduces circulating asparagine and interferes with protein synthesis in susceptible malignant cells.

Major toxicities include:

• Hypersensitivity/anaphylaxis
• Pancreatitis
• Hepatic dysfunction
• Hyperglycemia
• Thrombosis
• Bleeding/coagulopathy

Coagulation abnormalities reflect disruption of hepatic synthesis of both procoagulant and anticoagulant proteins.

12. Nitrosoureas

Carmustine and lomustine can produce particularly delayed myelosuppression.

Important effects include:

• Thrombocytopenia
• Leukopenia
• Pulmonary toxicity
• Hepatic injury
• Renal injury
• CNS effects at high exposure

Marrow nadir may occur several weeks after treatment.

Therefore, short ED observation cannot exclude serious toxicity.

13. Procarbazine

Procarbazine has weak monoamine oxidase-inhibiting properties.

Potential adverse effects include:

• Myelosuppression
• GI symptoms
• Neuropathy
• CNS disturbances

Clinically important medication and dietary interactions should be considered during therapy, although the interaction profile should not simply be extrapolated from classic irreversible MAO inhibitors.

14. Extravasation

Several antineoplastic drugs can cause substantial local tissue injury if they escape from the vein.

Possible manifestations include:

• Burning
• Pain
• Swelling
• Erythema
• Blistering
• Ulceration
• Tissue necrosis

Vesicants

Important vesicant drugs include:

• Anthracyclines
• Vinca alkaloids
• Mechlorethamine
• Mitomycin
• Several other cytotoxic agents

Management is drug specific.

Extravasation Management

General priorities include:

• Stop the infusion immediately
• Leave vascular access available initially when appropriate for aspiration/antidotal management
• Avoid flushing the infiltrated line
• Identify the exact drug
• Elevate the affected limb when appropriate
• Follow the agent-specific cold/warm compress protocol
• Obtain oncology/pharmacy/extravasation specialist guidance

The older recommendation to inject saline into the site to “dilute” the drug is not a universal modern approach and may spread the vesicant further.

Extravasation Antidotes

Depending on the drug, modern antidotal strategies may include:

• Dexrazoxane for anthracycline extravasation
• Hyaluronidase for selected vinca alkaloid/taxane extravasations
• Sodium thiosulfate for selected mechlorethamine-related injuries

Antidote choice, compress temperature, and technique are drug specific.

Routine corticosteroid infiltration is not a universal treatment.

Myelosuppression

Myelosuppression is one of the most important delayed complications of cytotoxic chemotherapy.

It can cause:

• Neutropenia → infection/sepsis
• Thrombocytopenia → bleeding
• Anemia → fatigue, dyspnea, tissue hypoxia

The timing of nadir differs substantially between agents.

Neutropenic Fever

Fever in a significantly neutropenic patient after chemotherapy is an oncologic emergency.

Management includes:

• Immediate clinical assessment
• Blood cultures and appropriate infection evaluation
• Prompt empiric antimicrobial therapy according to febrile-neutropenia protocols

Treatment should not be delayed while waiting for culture results.

Growth Factors

Granulocyte colony-stimulating factors such as filgrastim may be used in selected chemotherapy-associated neutropenia or overdose situations.

Use depends on:

• Agent involved
• Severity and expected duration of neutropenia
• Infection status
• Oncology/toxicology recommendations

A single historical neutrophil threshold is insufficient to determine use.

Laboratory Evaluation

Important baseline studies after significant antineoplastic overdose may include:

• CBC with differential
• Platelet count
• Electrolytes
• Glucose
• BUN/creatinine
• Liver tests

Additional studies depend on the drug.

Agent-Specific Testing

Methotrexate

• Serial methotrexate concentrations
• Creatinine
• Urine pH when high-dose toxicity is relevant

Cisplatin/carboplatin

• Magnesium
• Potassium
• Calcium
• Renal function
• Audiometry when indicated

Cyclophosphamide/ifosfamide

• Urinalysis
• Renal function
• Electrolytes
• Acid–base status

Anthracyclines

• ECG
• Cardiac biomarkers when clinically indicated
• Echocardiography for suspected myocardial dysfunction

Bleomycin

• Oxygenation
• Pulmonary imaging/function assessment when symptomatic

Serial CBC Is Essential

A normal initial CBC does not exclude future severe marrow suppression.

Repeat testing must be scheduled according to:

• Drug
• Dose
• Expected nadir
• Clinical condition

This is one of the most important follow-up principles in antineoplastic poisoning.

GI Decontamination

Do not induce vomiting.

Ipecac is obsolete.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a clinically important recent oral exposure when:

• The agent is adsorbable
• Airway protection is adequate
• Aspiration risk is acceptable
• Expected benefit outweighs risk

Many antineoplastic overdoses occur through parenteral medication errors, where GI decontamination has no role.

Seizures

For toxicologic seizures:

Benzodiazepines are first-line.

Persistent seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic therapy for refractory status epilepticus

Correct contributing:

• Hypoglycemia
• Electrolyte abnormalities
• Hypoxia
• Acid–base disturbances

Hypotension

Identify the mechanism, such as:

• Volume depletion
• Rapid infusion reaction
• Anaphylaxis
• Cardiogenic shock
• Sepsis
• Coingestant

Use appropriate isotonic fluid when indicated.

Vasopressor selection should be based on shock physiology; norepinephrine is generally preferred for persistent vasodilatory shock.

Trendelenburg positioning and routine dopamine-first therapy are outdated.

Dysrhythmias

There is no universal antineoplastic-associated dysrhythmia treatment.

Management depends on:

• Exact drug
• Rhythm
• QRS duration
• QT interval
• Electrolytes
• Myocardial function
• Hemodynamic stability

The older routine sequence of bicarbonate → lidocaine → bretylium is not a modern universal chemotherapy-overdose algorithm.

Bretylium is obsolete in routine contemporary resuscitation.

Dialysis and Extracorporeal Treatment

Extracorporeal removal is highly agent dependent.

It cannot be generalized across antineoplastic drugs.

For example, severe delayed methotrexate elimination is now approached with:

• Leucovorin
• Hydration
• Urinary alkalinization
• Glucarpidase when indicated

rather than assuming conventional dialysis is the optimal method of drug removal.

Renal replacement therapy remains appropriate for conventional severe renal/metabolic indications.

Monitoring

Significant antineoplastic overdose may require monitoring for:

• Delayed cytopenias
• Infection
• Bleeding
• Mucositis
• Renal failure
• Hepatic injury
• Electrolyte abnormalities
• Cardiac dysfunction
• Neurotoxicity
• Pulmonary toxicity

The monitoring period can extend for days to weeks depending on the agent.

Disposition

A universal “6-hour observation then discharge” approach is inappropriate.

Disposition depends on:

• Exact drug
• Dose
• Route
• Time since exposure
• Renal/hepatic function
• Initial symptoms
• Expected delayed toxicity
• Ability to obtain serial laboratory testing
• Reliability of oncology/toxicology follow-up

A clinically well patient may still require carefully scheduled outpatient CBC and organ-function monitoring.

Admission

Hospitalization is appropriate for clinically important exposures associated with:

• Significant methotrexate accumulation
• Severe mucositis
• Neutropenia
• Febrile neutropenia
• Thrombocytopenia/bleeding
• Severe anemia
• AKI
• Major electrolyte abnormalities
• Hepatic failure
• Encephalopathy
• Seizures
• Cardiac toxicity
• Pulmonary toxicity
• Serious extravasation
• Significant fluoropyrimidine overdose

ICU care may be necessary for shock, respiratory failure, malignant dysrhythmia, status epilepticus, severe sepsis, or multiorgan failure.

Pregnancy

The historical FDA pregnancy letter categories are obsolete.

Many traditional cytotoxic antineoplastics can cause:

• Embryotoxicity
• Fetotoxicity
• Teratogenicity
• Fetal growth effects

However, cancer treatment during pregnancy is highly dependent on:

• Specific drug
• Gestational age
• Cancer type
• Disease urgency
• Treatment alternatives

Pregnancy is therefore not appropriately summarized by a single class-wide prohibition.

Safeguarding and Medication Error

Antineoplastic overdose is frequently iatrogenic, making systems analysis important.

Potential causes include:

• Wrong dose
• Wrong route
• Wrong infusion rate
• Wrong schedule
• Confusion between daily and weekly dosing
• Intrathecal/intravenous route errors
• Pump programming errors

Prevention and rapid recognition of chemotherapy medication errors are major components of toxicology care.

Rigid age cutoffs for assuming abuse or intentional poisoning are outdated.

Prognosis

Outcome varies enormously by drug and exposure.

Important causes of morbidity and mortality include:

• Neutropenic sepsis
• Severe thrombocytopenic bleeding
• Multiorgan failure
• AKI
• Cardiomyopathy
• Pulmonary fibrosis
• Severe neurotoxicity
• Catastrophic wrong-route administration

Some complications may be permanent, including:

• Peripheral neuropathy
• Hearing loss
• Cardiac dysfunction
• Pulmonary fibrosis
• CNS injury
• Renal impairment

Important Modernization of the Older Source

• Antineoplastic poisoning is highly agent- and route-specific.
• Early asymptomatic appearance does not exclude serious delayed toxicity.
• Serial CBC monitoring is crucial because myelosuppression may be delayed.
• Methotrexate toxicity requires protocol-guided leucovorin rescue, hydration, urinary alkalinization, and serial concentrations.
• Glucarpidase is an important modern treatment for selected high-dose methotrexate toxicity with renal dysfunction and delayed elimination.
• Repeated accidental daily methotrexate dosing is an important modern poisoning pattern.
• Uridine triacetate is the specific emergency antidotal therapy for selected 5-FU/capecitabine overdoses and early severe fluoropyrimidine toxicity.
• DPD deficiency can produce catastrophic fluoropyrimidine toxicity at otherwise therapeutic exposure.
• Mesna prevents urothelial injury from ifosfamide and selected cyclophosphamide regimens.
• Ifosfamide can cause severe encephalopathy.
• Dexrazoxane has roles in anthracycline cardioprotection and anthracycline extravasation.
• Intrathecal vincristine is a catastrophic, potentially fatal wrong-route error.
• Extravasation treatment is drug specific; saline injection to dilute a vesicant is not a universal modern recommendation.
• Bleomycin exposure does not mean withholding oxygen from a hypoxemic patient.
• Fever with significant chemotherapy-induced neutropenia requires urgent empiric infection management.
• G-CSF decisions should be individualized rather than based on one historic cell-count threshold.
• The historical bicarbonate/lidocaine/bretylium sequence is not a universal treatment for chemotherapy-related dysrhythmia; bretylium is obsolete.
• Ipecac and routine gastric lavage are obsolete.
• Trendelenburg and dopamine-first shock management are outdated.
• Fixed 6-hour observation is inadequate for drugs with delayed marrow or organ toxicity.
• Historical FDA pregnancy categories are obsolete.

Key Points

• Antineoplastic toxicity is drug-, dose-, route-, and time-dependent.
• Delayed myelosuppression is one of the most important dangers.
• Methotrexate → leucovorin rescue; glucarpidase for selected severe delayed elimination with renal dysfunction.
• 5-FU/capecitabine → uridine triacetate for qualifying overdose or early severe toxicity.
• Cisplatin → nephrotoxicity, electrolyte wasting, ototoxicity, neuropathy.
• Cyclophosphamide/ifosfamide → hemorrhagic cystitis; mesna is protective.
• Ifosfamide → encephalopathy.
• Anthracyclines → cardiotoxicity and severe extravasation injury.
• Vincristine → neurotoxicity; intrathecal administration is catastrophic.
• Bleomycin → pulmonary toxicity.
• Asparaginase → pancreatitis, coagulopathy/thrombosis, hyperglycemia, hypersensitivity.
• A normal early CBC does not rule out later severe toxicity.
• Significant exposures require early toxicology, oncology, pharmacy, and poison-center coordination with prolonged follow-up when indicated.

Toxicology – Sulfonamides

Core Concept

Sulfonamides include several antimicrobial drugs and related compounds. Important examples include:

• Sulfamethoxazole, most commonly combined with trimethoprim as TMP-SMX
• Sulfadiazine
• Sulfadoxine
• Sulfacetamide
• Silver sulfadiazine
• Mafenide
• Sulfasalazine — primarily used for inflammatory bowel disease and some rheumatologic conditions

Many older sulfonamides are now rarely used.

Acute isolated overdose is usually relatively mild. More clinically important toxicity generally occurs as an adverse reaction during therapeutic use, particularly:

• Hypersensitivity
• Severe cutaneous adverse reactions
• Hematologic toxicity
• Renal injury
• Hepatotoxicity
• Hyperkalemia from the trimethoprim component of TMP-SMX
• Hypoglycemia in susceptible patients
• Rare methemoglobinemia or hemolysis

There is no universal specific antidote for sulfonamide poisoning.

Mechanism of Antimicrobial Action

Sulfonamide antibiotics inhibit bacterial folate synthesis by competing with para-aminobenzoic acid (PABA) and inhibiting dihydropteroate synthase.

Trimethoprim acts at a different step by inhibiting dihydrofolate reductase.

Therefore, TMP-SMX produces sequential inhibition of microbial folate metabolism.

Acute Overdose

Most isolated acute sulfonamide ingestions produce either no symptoms or relatively nonspecific GI effects such as:

• Nausea
• Vomiting
• Abdominal discomfort

Severe acute toxicity is uncommon.

Importantly, many of the most serious sulfonamide reactions are not directly related to the size of an overdose.

1. Hypersensitivity

Sulfonamide antimicrobials can cause immune-mediated reactions at therapeutic doses.

Possible manifestations include:

• Fever
• Maculopapular rash
• Urticaria
• Angioedema
• Drug fever
• Rare anaphylaxis

A susceptible individual can react after relatively small exposure, so there is no meaningful “safe overdose threshold” for allergic reactions.

Severe Cutaneous Adverse Reactions

Sulfonamide antibiotics are important causes of severe drug eruptions, including:

• Stevens–Johnson syndrome (SJS)
• Toxic epidermal necrolysis (TEN)
• DRESS
• AGEP

These are primarily delayed adverse drug reactions rather than manifestations of acute overdose.

SJS/TEN

Warning features include:

• Fever
• Malaise
• Painful skin
• Blistering
• Epidermal detachment
• Oral erosions
• Ocular involvement
• Genital mucosal involvement

Suspected SJS/TEN requires:

Immediate discontinuation of the causative drug + urgent hospital assessment + supportive specialist care

Simply treating the eruption as an uncomplicated “sulfa allergy” can miss a life-threatening syndrome.

DRESS

Drug reaction with eosinophilia and systemic symptoms may produce:

• Fever
• Extensive rash
• Facial edema
• Eosinophilia
• Lymphadenopathy
• Hepatitis
• Nephritis
• Other organ involvement

Symptoms may continue or evolve even after the medication has been discontinued.

“Sulfa Allergy” – Important Clarification

A history of allergy to a sulfonamide antimicrobial does not automatically mean that the patient will cross-react with every medication containing a sulfonamide chemical group.

Non-antimicrobial sulfonamide-containing drugs are structurally different.

Therefore:

“Sulfa allergy” should not automatically be interpreted as allergy to all sulfur-containing or sulfonamide-containing medications.

Elemental sulfur, sulfates, and sulfites are also chemically distinct from sulfonamide antibiotics.

2. Renal Toxicity

Sulfonamides are substantially eliminated through the kidneys, and renal impairment can increase systemic exposure to some agents.

Renal complications include:

• Crystalluria
• Crystal nephropathy
• Hematuria
• Acute interstitial nephritis
• Acute kidney injury

Crystalluria

Some sulfonamides or their metabolites have limited urinary solubility.

Precipitation within the urinary tract can produce:

Crystalluria → tubular obstruction/injury → hematuria → AKI

Risk may increase with:

• High exposure
• Dehydration
• Concentrated urine
• Preexisting renal dysfunction

Modern agents are generally less prone to severe crystalluria than some older sulfonamides, but the complication remains possible.

Acute Interstitial Nephritis

Sulfonamides can cause immune-mediated interstitial nephritis.

Possible findings include:

• Rising creatinine
• Hematuria
• Pyuria
• Proteinuria

Fever, rash, and eosinophilia may occur but are not reliably present.

TMP-SMX and Creatinine – Important Pitfall

Trimethoprim can inhibit tubular secretion of creatinine.

Therefore, serum creatinine may rise even without a true fall in GFR.

This can create an apparent AKI.

However, TMP-SMX can also cause genuine renal injury, so a creatinine increase should not automatically be dismissed as a benign laboratory effect.

Interpret:

• Creatinine trend
• Urine output
• Urinalysis
• Electrolytes
• Overall clinical condition

3. Hyperkalemia

A major modern toxicity omitted from many older sulfonamide discussions is trimethoprim-associated hyperkalemia.

Trimethoprim can act similarly to the potassium-sparing diuretic amiloride in the distal nephron.

This decreases renal potassium excretion.

Therefore:

Trimethoprim → reduced K⁺ excretion → hyperkalemia

Risk Factors for TMP-SMX Hyperkalemia

Risk increases with:

• Renal impairment
• Older age
• High trimethoprim exposure
• Baseline hyperkalemia
• ACE inhibitors
• ARBs
• Potassium-sparing diuretics
• Other medications that impair potassium elimination

Severe hyperkalemia can cause:

• Weakness
• Conduction abnormalities
• Ventricular dysrhythmia
• Cardiac arrest

Hyperkalemia Management

Clinically important hyperkalemia should be managed according to severity and ECG findings.

Priorities include:

• Stop contributing medications
• Cardiac stabilization when indicated
• Shift potassium intracellularly
• Promote potassium elimination
• Consider dialysis for severe refractory hyperkalemia or major renal failure

The serum potassium level and clinical/ECG picture are more important than the size of the original antibiotic exposure.

4. Hematologic Toxicity

Sulfonamides can rarely cause:

• Neutropenia
• Agranulocytosis
• Thrombocytopenia
• Pancytopenia
• Hemolytic anemia

These are generally complications of therapeutic exposure rather than isolated acute ingestion.

Hemolysis and G6PD Deficiency

Sulfonamide antimicrobials can produce oxidative stress.

Patients with G6PD deficiency may be more susceptible to hemolysis.

Possible findings include:

• Fatigue
• Pallor
• Jaundice
• Dark urine
• Falling hemoglobin
• Elevated bilirubin
• Elevated LDH
• Reduced haptoglobin

The risk varies by drug, dose, and individual susceptibility.

5. Methemoglobinemia

Methemoglobinemia is an uncommon but recognized complication of some sulfonamide exposures.

Oxidation converts hemoglobin iron:

Fe²⁺ → Fe³⁺

Methemoglobin cannot effectively carry oxygen.

Clinical Features of Methemoglobinemia

Possible findings include:

• Cyanosis
• Headache
• Dizziness
• Dyspnea
• Fatigue
• Tachycardia

Severe cases may cause:

• Altered consciousness
• Myocardial ischemia
• Seizures
• Dysrhythmias
• Cardiovascular collapse

Diagnosis of Methemoglobinemia

A characteristic clue is:

Low pulse oximetry that improves little despite supplemental oxygen

Blood may appear unusually dark or brownish.

Diagnosis is confirmed using co-oximetry.

Standard pulse oximetry alone cannot accurately quantify methemoglobin.

Treatment of Methemoglobinemia

Management includes:

• Stop the oxidizing drug
• Supplemental oxygen
• Support airway and circulation
• Treat clinically significant symptomatic methemoglobinemia with an appropriate reducing agent such as methylene blue

Treatment decisions depend on:

• Symptoms
• Methemoglobin concentration
• Comorbid disease
• Evidence of tissue hypoxia

A rigid concentration alone should not determine treatment.

Methylene Blue – Important Caution

Methylene blue requires particular caution in patients with G6PD deficiency because:

• Response may be reduced
• Hemolysis may worsen

It can also contribute to serotonergic toxicity because it has monoamine oxidase-inhibiting properties.

Severe cases in which methylene blue is ineffective or unsuitable require specialist toxicology/hematology input.

6. Hypoglycemia

Sulfonamide antimicrobial therapy, especially TMP-SMX, can occasionally cause hypoglycemia.

Risk increases with:

• Renal impairment
• Malnutrition
• Older age
• High systemic exposure
• Concurrent glucose-lowering medications

Manifestations include:

• Sweating
• Tremor
• Confusion
• Altered consciousness
• Seizures

Check bedside glucose in patients with neurologic symptoms.

7. Hepatotoxicity

Sulfonamide antibiotics can cause drug-induced liver injury.

Patterns may include:

• Hepatocellular injury
• Cholestatic injury
• Mixed injury

Liver involvement can also occur as part of systemic hypersensitivity or DRESS.

Clinical Features of Liver Injury

Possible findings include:

• Fatigue
• Nausea
• Right-upper-quadrant discomfort
• Pruritus
• Dark urine
• Jaundice

Evaluation may include:

• AST/ALT
• Bilirubin
• Alkaline phosphatase
• Coagulation studies when severe

8. Pulmonary Hypersensitivity

Rare pulmonary reactions include:

• Drug-induced pneumonitis
• Eosinophilic pulmonary reactions
• Other hypersensitivity lung injury

Symptoms may include:

• Cough
• Dyspnea
• Fever
• Hypoxemia

Alternative infectious and cardiopulmonary causes must also be considered.

9. Sulfasalazine

Sulfasalazine deserves separate consideration because it is metabolized in the colon to:

• 5-aminosalicylic acid
• Sulfapyridine

Therefore, its toxicity is not identical to ordinary sulfonamide antimicrobial poisoning.

Possible adverse effects include:

• Nausea
• Vomiting
• Abdominal discomfort
• Headache
• Rash
• Hepatotoxicity
• Hematologic toxicity
• Rare hemolysis
• Rare severe hypersensitivity

Large exposures may also have features related to its salicylate-derived component, although classic severe salicylate poisoning should not automatically be assumed.

10. Topical Sulfonamides

Silver Sulfadiazine

Used particularly for selected burn/wound indications.

Systemic absorption can occur when applied to large areas of damaged skin.

Potential complications include:

• Leukopenia
• Hypersensitivity
• Rare systemic sulfonamide effects

Mafenide

Mafenide is particularly important because it can inhibit carbonic anhydrase.

Systemic absorption from large treated burn areas can contribute to:

Bicarbonate loss → hyperchloremic metabolic acidosis

This is an important agent-specific toxicity not emphasized in older general sulfonamide summaries.

11. Neonates and Bilirubin

Sulfonamides have historically raised concern for displacement of bilirubin from albumin binding.

Neonates—particularly premature infants or those with significant hyperbilirubinemia—require special caution because excessive unbound bilirubin can contribute to bilirubin encephalopathy/kernicterus.

This concern is primarily relevant to systemic therapeutic exposure in susceptible neonates rather than typical accidental overdose in older children.

Pregnancy and Breastfeeding

The old FDA pregnancy letter categories are obsolete.

Use during pregnancy should be individualized according to:

• Specific drug
• Gestational timing
• Infection
• Maternal condition
• Folate considerations
• Available alternatives

TMP-SMX deserves particular consideration because trimethoprim interferes with folate metabolism.

Near delivery, neonatal bilirubin-related considerations may also influence drug selection.

Breastfeeding

Sulfonamide use during breastfeeding should consider:

• Infant age
• Prematurity
• Hyperbilirubinemia
• G6PD status
• Specific medication

A blanket statement that all sulfonamides are either completely safe or universally contraindicated during breastfeeding is inappropriate.

Diagnosis

Determine:

• Exact product
• Whether trimethoprim is also present
• Amount
• Timing
• Acute vs prolonged exposure
• Renal function
• Other medications
• Allergy history
• Coingestants

The distinction between isolated sulfonamide exposure and TMP-SMX is particularly important because trimethoprim contributes additional renal and electrolyte effects.

Laboratory Evaluation

Small asymptomatic exposures may require no testing.

For significant or symptomatic toxicity, consider:

• Bedside glucose
• CBC
• Electrolytes
• Potassium
• Bicarbonate
• BUN/creatinine
• Urinalysis
• Liver tests

Depending on presentation:

• Co-oximetry for suspected methemoglobinemia
• Hemolysis studies
• ECG for hyperkalemia or significant systemic illness
• Blood gas when severe acid–base disturbance is suspected

Serum Sulfonamide Concentrations

Routine serum sulfonamide concentrations are generally not clinically useful.

Management should be guided by:

• Symptoms
• Renal function
• Electrolytes
• Hematologic findings
• Organ injury

Initial Management

General priorities are:

Airway/breathing → circulation → identify exact drug → glucose → electrolytes/renal function → evaluate hypersensitivity and organ toxicity → supportive care

Most isolated acute ingestions do not require aggressive intervention.

GI Decontamination

Do not induce vomiting.

Ipecac has no modern role.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a substantial recent ingestion when:

• The drug is adsorbable
• The airway is safe
• Aspiration risk is acceptable
• Expected clinical benefit justifies treatment

Many uncomplicated exposures require no decontamination.

Anaphylaxis

If true anaphylaxis occurs:

IM epinephrine is first-line therapy.

Provide:

• Airway support
• Oxygen when required
• Appropriate IV fluid resuscitation
• Additional supportive treatment

Antihistamines may help skin symptoms but must not delay epinephrine.

Seizures

For toxicologic seizures:

Benzodiazepines are first-line.

Persistent seizures may require additional benzodiazepines, phenobarbital, or appropriate anesthetic management.

Correct accompanying:

• Hypoglycemia
• Electrolyte abnormalities
• Hypoxia
• Acid–base disturbances

Hypotension

Determine whether hypotension reflects:

• Anaphylaxis
• Dehydration
• Severe hypersensitivity
• Coingestion
• Other illness

Treat appropriate volume depletion with isotonic crystalloid.

Persistent vasodilatory shock generally favors norepinephrine.

Trendelenburg positioning and routine dopamine-first therapy are outdated.

Renal Management

When crystalluria or renal injury is suspected:

• Stop further exposure
• Correct dehydration appropriately
• Monitor renal function
• Monitor urine output
• Correct electrolyte abnormalities
• Avoid additional nephrotoxins where possible

Aggressive forced diuresis is not routinely appropriate.

Enhanced Elimination

Hemodialysis is not routine treatment for uncomplicated sulfonamide overdose.

It may become relevant when severe toxicity occurs in the setting of:

• Major renal failure
• Severe refractory electrolyte abnormalities
• Other conventional indications for renal replacement therapy

The decision should be individualized.

Monitoring

Monitoring should match the toxicity.

Renal toxicity

• Creatinine
• Electrolytes
• Potassium
• Urine output

Hematologic toxicity

• CBC
• Hemolysis studies when indicated

Hepatotoxicity

• Liver tests
• Coagulation studies if severe

Methemoglobinemia

• Clinical oxygenation
• Co-oximetry

Severe hypersensitivity

• Skin/mucosal progression
• Airway
• Hemodynamics
• Organ involvement

Observation and Disposition

There is no universal observation period.

Disposition depends on:

• Exact drug
• Amount
• Symptoms
• Renal function
• Potassium/glucose abnormalities
• Coingestants
• Clinical trajectory

Importantly, delayed immune reactions such as SJS/TEN, DRESS, cytopenias, or hepatitis cannot be excluded by a few hours of emergency observation.

Admission

Hospitalization may be required for:

• Anaphylaxis
• SJS/TEN or other severe cutaneous reaction
• DRESS with organ involvement
• Significant methemoglobinemia
• Hemolysis
• Severe cytopenia
• AKI
• Significant hyperkalemia
• Severe hypoglycemia
• Hepatic injury
• Persistent seizures
• Hemodynamic instability

ICU or specialized burn/critical-care management may be necessary for severe SJS/TEN, shock, respiratory failure, or major methemoglobinemia.

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional poisoning are outdated.

Pediatric exposures should instead be assessed according to:

• Developmental capability
• Medication accessibility
• Circumstances
• Consistency of history
• Recurrent unexplained exposures
• Broader safeguarding concerns

Prognosis

Most isolated acute sulfonamide ingestions recover with supportive care.

Prognosis is more serious when toxicity involves:

• SJS/TEN
• DRESS
• Severe anaphylaxis
• Agranulocytosis
• Severe hemolysis
• Methemoglobinemia
• Significant AKI
• Hyperkalemia
• Severe hepatic injury

Important Modernization of the Older Source

• Acute sulfonamide overdose is usually mild, while serious toxicity more often represents therapeutic adverse reactions.
• Hypersensitivity is not reliably dose dependent; severe reactions can occur at therapeutic doses.
• Sulfonamide antimicrobials are important causes of SJS/TEN and DRESS.
• “Sulfa allergy” does not automatically imply cross-allergy to every non-antibiotic sulfonamide, sulfate, sulfite, or sulfur-containing substance.
• TMP-SMX must be considered as a two-drug exposure.
• Trimethoprim can cause clinically important hyperkalemia.
• Trimethoprim may raise serum creatinine by reducing tubular creatinine secretion without necessarily reducing true GFR.
• Sulfonamides can also cause true AKI through crystal nephropathy or interstitial nephritis.
• G6PD deficiency may increase susceptibility to oxidative hemolysis.
• Methemoglobinemia is rare but potentially serious; diagnosis is by co-oximetry.
• Methylene blue requires special caution in G6PD deficiency and can interact with serotonergic medications.
• Mafenide can cause hyperchloremic metabolic acidosis through carbonic-anhydrase inhibition.
• Neonatal kernicterus concerns are primarily relevant to susceptible premature or hyperbilirubinemic infants.
• Ipecac and routine gastric lavage are obsolete.
• Forced diuresis is not routine treatment for crystalluria.
• Trendelenburg and dopamine-first shock management are outdated.
• Historical FDA pregnancy letter categories are obsolete.
• Delayed hypersensitivity, marrow, liver, and renal complications cannot be excluded by a short observation period.

Key Points

• Sulfonamides → hypersensitivity, renal, hematologic, and hepatic toxicity.
• TMP-SMX → remember trimethoprim-associated hyperkalemia and creatinine elevation.
• SJS/TEN and DRESS are major delayed adverse reactions.
• Crystalluria, interstitial nephritis, and true AKI can occur.
• G6PD deficiency increases concern for oxidative hemolysis.
• Rare methemoglobinemia is confirmed with co-oximetry.
• Mafenide → hyperchloremic metabolic acidosis.
• Sulfonamide allergy does not equal allergy to all sulfur-containing drugs.
• There is no single specific antidote for sulfonamide poisoning.
• Management is primarily withdrawal of the offending drug, supportive care, and targeted treatment of complications.

Toxicology – Penicillins and Cephalosporins

Core Concept

Penicillins and cephalosporins are β-lactam antibiotics. Acute oral overdose is usually mild, but important toxicity can occur with very large exposure, parenteral dosing errors, renal impairment, or hypersensitivity.

Major toxicologic concerns are:

• GI upset
• Hypersensitivity and anaphylaxis
• Neurotoxicity → encephalopathy, myoclonus, seizures
• Renal injury/crystalluria with selected agents
• Electrolyte disturbances from certain formulations
• Selected cephalosporin-associated coagulopathy
• Rare hematologic and hepatic reactions

There is no specific antidote for β-lactam overdose.

⸻

Major Penicillins

Important examples include:

• Penicillin G
• Penicillin V
• Amoxicillin
• Ampicillin
• Amoxicillin-clavulanate
• Ampicillin-sulbactam
• Flucloxacillin/dicloxacillin
• Nafcillin
• Oxacillin
• Piperacillin-tazobactam

Some agents in older references, such as methicillin, carbenicillin, and ticarcillin, are now rarely used or unavailable in many regions.

⸻

Major Cephalosporins

Examples include:

• Cephalexin
• Cefazolin
• Cefuroxime
• Ceftriaxone
• Cefotaxime
• Ceftazidime
• Cefepime
• Cefixime
• Cefpodoxime

Newer cephalosporin-containing therapies also exist, including agents active against resistant organisms.

Toxicity varies somewhat among individual drugs.

⸻

Mechanism

β-Lactams inhibit bacterial cell-wall synthesis by binding penicillin-binding proteins (PBPs) and interfering with peptidoglycan cross-linking.

This antibacterial mechanism does not directly explain most human toxicity.

⸻

Acute Oral Overdose

Most isolated oral exposures cause either no symptoms or:

• Nausea
• Vomiting
• Diarrhea
• Abdominal discomfort

A single historical dose threshold should not be used to determine whether toxicity will occur.

Risk assessment should instead consider:

• Exact drug
• Amount
• Route
• Renal function
• Symptoms
• Coingestants
• Formulation
• Patient-specific factors

⸻

1. Hypersensitivity

All β-lactams can produce allergic reactions.

Manifestations range from:

• Mild maculopapular rash
• Urticaria
• Angioedema

to severe:

• Bronchospasm
• Upper-airway edema
• Hypotension
• Anaphylaxis

Importantly, allergic reactions are not dose dependent and can occur after relatively small therapeutic exposures.

⸻

Anaphylaxis

Possible findings include:

• Urticaria/flushing
• Angioedema
• Wheezing
• Stridor
• Respiratory distress
• Vomiting
• Hypotension
• Cardiovascular collapse

Epinephrine is first-line treatment for anaphylaxis.

Airway and circulatory support should occur simultaneously as required.

Antihistamines are only adjunctive treatments and must not delay epinephrine.

Routine H2-blocker treatment is no longer a central component of emergency anaphylaxis management.

⸻

Anaphylaxis – Important Update

The older recommendation for subcutaneous epinephrine is outdated.

For most anaphylaxis:

Intramuscular epinephrine is the preferred initial route.

IV epinephrine is reserved for selected severe refractory cases under closely monitored expert management because dosing errors can cause dangerous hypertension and dysrhythmias.

⸻

Penicillin–Cephalosporin Cross-Reactivity

The historical claim that patients with penicillin allergy have approximately a 10% risk of reacting to first-generation cephalosporins substantially overstates modern estimates.

Cross-reactivity depends importantly on:

• Whether the original allergy was genuine
• Type of reaction
• β-lactam structure
• R1 side-chain similarity

Many patients carrying a “penicillin allergy” label are not truly allergic.

⸻

Clinical Importance of Side Chains

Cross-reactivity is more likely when the penicillin and cephalosporin have similar side chains.

Therefore, β-lactam allergy assessment should be drug-specific, rather than assuming all penicillins and cephalosporins cross-react equally.

⸻

2. Neurotoxicity

β-Lactams can produce CNS toxicity, particularly when excessive concentrations accumulate.

Manifestations include:

• Confusion
• Agitation
• Encephalopathy
• Myoclonus
• Hallucinations
• Seizures
• Nonconvulsive status epilepticus
• Coma in severe cases

⸻

Mechanism of β-Lactam Neurotoxicity

At excessive CNS concentrations, β-lactams can interfere with inhibitory GABAergic neurotransmission.

This helps explain their proconvulsant effects.

⸻

Risk Factors for Neurotoxicity

Important risk factors include:

• Renal impairment
• Failure to adjust dose for kidney function
• Older age
• High parenteral doses
• Preexisting CNS disease
• Critical illness

Neurotoxicity during therapeutic use is therefore frequently a problem of drug accumulation, not intentional overdose.

⸻

Cefepime Neurotoxicity

Cefepime deserves particular attention.

Accumulation can produce:

• Altered mental status
• Encephalopathy
• Aphasia
• Myoclonus
• Seizures
• Nonconvulsive status epilepticus

Renal impairment is a major risk factor.

⸻

Recognizing Cefepime Neurotoxicity

Suspect it when a patient receiving cefepime—especially with reduced renal function—develops otherwise unexplained:

• Confusion
• Reduced consciousness
• Myoclonus
• Seizure activity

EEG may demonstrate abnormalities including patterns compatible with toxic-metabolic encephalopathy or nonconvulsive seizures.

Clinical context is essential because EEG findings are not specific to cefepime.

⸻

Management of β-Lactam Neurotoxicity

The major intervention is:

Stop or appropriately reduce the offending β-lactam and correct drug accumulation.

For seizures:

Benzodiazepines are first-line.

Persistent seizures may require additional benzodiazepines, phenobarbital, or appropriate anesthetic treatment for refractory status epilepticus.

Phenytoin is generally not preferred as routine treatment for toxicologic seizures.

⸻

3. Renal Toxicity

Several β-lactams can cause renal injury through different mechanisms.

These include:

• Crystalluria/crystal nephropathy
• Acute interstitial nephritis
• Hemodynamic or multifactorial AKI during severe illness

⸻

Amoxicillin Crystal Nephropathy

High urinary concentrations of amoxicillin can produce crystal precipitation.

Possible consequences include:

• Crystalluria
• Hematuria
• Flank discomfort
• Oliguria
• Acute kidney injury

Risk increases with high exposure and clinical circumstances favoring concentrated urine.

⸻

Ampicillin/Amoxicillin and AKI

Very high exposure may therefore produce renal dysfunction, but the mechanism should not simply be described as universal “tubular toxicity.”

Crystal-related obstruction and interstitial nephritis are important mechanisms to consider.

⸻

Acute Interstitial Nephritis

β-Lactams are recognized causes of drug-induced acute interstitial nephritis.

Possible findings include:

• Rising creatinine
• Hematuria
• Pyuria
• Proteinuria

The classic combination of:

fever + rash + eosinophilia

may occur but is absent in many patients.

⸻

Renal Evaluation

In significant exposure or symptomatic patients, consider:

• Creatinine
• BUN
• Electrolytes
• Urinalysis
• Urine output

Renal function is especially important when neurologic toxicity is present because reduced clearance can markedly increase β-lactam concentrations.

⸻

4. Electrolyte Toxicity

Certain IV penicillin formulations contain substantial amounts of sodium or potassium.

Thus, toxicity may partly reflect the counter-ion rather than the antibiotic itself.

⸻

Potassium Penicillin G

Rapid or excessive administration of potassium-containing penicillin formulations can contribute to:

• Hyperkalemia
• Conduction abnormalities
• Ventricular dysrhythmia
• Cardiac arrest

This is mainly relevant to parenteral medication errors rather than ordinary oral penicillin exposure.

⸻

Sodium Load

High-dose sodium-containing β-lactam therapy can contribute to:

• Sodium load
• Fluid retention
• Electrolyte disturbance

This is particularly relevant in patients with:

• Heart failure
• Renal dysfunction
• Other conditions sensitive to sodium load

⸻

5. Cephalosporin-Associated Coagulopathy

Certain cephalosporins, particularly some containing an N-methylthiotetrazole (NMTT) side chain, can impair vitamin K–dependent coagulation.

Possible consequences include:

• Prolonged PT/INR
• Hypoprothrombinemia
• Bleeding

Historically important agents include cefotetan and cefoperazone, among others.

⸻

Risk Factors for Coagulopathy

Risk increases with:

• Malnutrition
• Prolonged antibiotic therapy
• Reduced vitamin K intake
• Significant liver disease
• Other causes of coagulopathy

This is generally a complication of therapeutic exposure rather than an acute single overdose.

⸻

Management of Cephalosporin Coagulopathy

Management includes:

• Stop/reassess the causative drug
• Measure coagulation studies
• Correct vitamin K deficiency when present
• Treat clinically significant bleeding using appropriate blood-product or factor replacement strategies

Routine prophylactic vitamin K is not required after every cephalosporin exposure.

⸻

6. Cephalosporins and Ethanol

Some NMTT-containing cephalosporins have historically been associated with a disulfiram-like reaction after alcohol exposure.

Possible symptoms include:

• Flushing
• Headache
• Nausea
• Vomiting
• Tachycardia
• Hypotension

This is agent-specific and should not be generalized to all cephalosporins.

⸻

7. Ceftriaxone

Ceftriaxone has several distinctive adverse effects.

These include:

• Biliary sludge/pseudolithiasis
• Rare immune hemolytic anemia
• Precipitation interactions with calcium in specific clinical circumstances

These are therapeutic adverse effects rather than the expected syndrome after a simple acute ingestion.

⸻

Immune Hemolytic Anemia

Ceftriaxone can rarely cause severe immune-mediated hemolysis.

Possible findings include:

• Sudden anemia
• Pallor
• Jaundice
• Hemoglobinuria
• Tachycardia
• Hypotension

This can occasionally be severe and requires immediate discontinuation and supportive hematologic management.

⸻

8. Serum Sickness–Like Reaction

Cefaclor is particularly associated with serum sickness–like reactions, especially in children.

Features may include:

• Fever
• Rash
• Arthralgia
• Joint swelling

This differs from classic immune-complex serum sickness and usually improves after the offending medication is stopped.

⸻

9. Severe Cutaneous Reactions

Penicillins and cephalosporins can rarely produce severe delayed hypersensitivity syndromes such as:

• Stevens–Johnson syndrome
• Toxic epidermal necrolysis
• DRESS
• AGEP

These are not predictable from the size of an acute overdose.

⸻

Amoxicillin/Ampicillin Rash

A maculopapular rash is particularly common when aminopenicillins are given in the setting of certain viral illnesses, classically infectious mononucleosis.

Such a rash does not automatically establish an IgE-mediated penicillin allergy.

⸻

10. Procaine Penicillin Reaction

Procaine penicillin can rarely cause an acute neuropsychiatric syndrome historically termed the Hoigné syndrome.

Features may include:

• Severe anxiety
• Agitation
• Confusion
• Hallucinations
• Perceptual disturbance
• Seizure-like manifestations

It is associated with parenteral procaine penicillin administration rather than ordinary oral β-lactam poisoning.

⸻

GI Effects

The most common acute effects remain:

• Nausea
• Vomiting
• Diarrhea
• Abdominal pain

Antibiotic-associated alteration of intestinal flora can also lead to C. difficile infection, particularly after broader-spectrum or prolonged therapy.

⸻

Diagnosis

Determine:

• Exact β-lactam
• Formulation
• Route
• Amount
• Time of exposure
• Renal function
• Allergy history
• Other medications
• Coingestants

In a patient receiving therapeutic β-lactams who develops new encephalopathy or seizures, specifically review whether dosing has been appropriately adjusted for renal function.

⸻

Laboratory Evaluation

No laboratory testing is usually required after a minor, uncomplicated oral exposure.

For significant toxicity, consider:

• Glucose
• Electrolytes
• Potassium
• Creatinine/BUN
• CBC
• Urinalysis

Additional testing is directed by the syndrome.

For example:

• PT/INR when coagulopathy is suspected
• Hemolysis studies for suspected ceftriaxone immune hemolysis
• ECG with significant electrolyte abnormality or parenteral dosing error
• EEG for unexplained encephalopathy/myoclonus or suspected nonconvulsive status

⸻

Serum β-Lactam Concentrations

Routine serum penicillin or cephalosporin concentrations are generally unnecessary in acute poisoning.

Clinical status and renal function are usually more informative.

Specialized therapeutic drug monitoring may be used in selected critically ill patients, but this is different from routine toxicology testing.

⸻

Laboratory Interference

Some older cephalosporins can interfere with certain laboratory assays, including older creatinine methodologies.

When laboratory results appear inconsistent with the clinical picture, analytical interference should be considered.

⸻

Initial Management

The general approach is:

Airway/breathing → circulation → identify drug and route → assess renal function → evaluate neurologic status → treat hypersensitivity/seizures/electrolyte abnormalities

Most acute oral exposures require only supportive care.

⸻

GI Decontamination

Do not induce vomiting.

Ipecac has no modern role.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a substantial recent ingestion when:

• The drug is adsorbable
• The airway is safe
• Aspiration risk is low
• Expected benefit justifies treatment

Because most isolated β-lactam ingestions are benign, charcoal is unnecessary in many cases.

⸻

Hypotension

Determine whether hypotension is caused by:

• Anaphylaxis
• Dehydration
• Sepsis
• Dysrhythmia
• Coingestant

Appropriate isotonic crystalloid can be used when indicated.

Persistent vasodilatory shock generally favors norepinephrine.

Trendelenburg positioning and automatic dopamine-first therapy are outdated.

⸻

Anaphylaxis Management

Priorities include:

• IM epinephrine first
• Airway support
• Oxygen when required
• IV fluid resuscitation for hypotension
• Bronchodilator for persistent bronchospasm

Antihistamines may improve cutaneous symptoms but are adjuncts only.

Corticosteroids do not provide immediate reversal of life-threatening anaphylaxis and should never delay epinephrine.

⸻

Enhanced Elimination

There is no single extracorporeal recommendation for every β-lactam.

Several β-lactams are substantially renally eliminated and some can be removed by hemodialysis.

This becomes most relevant when there is:

• Severe renal failure
• Marked drug accumulation
• Severe persistent neurotoxicity
• Conventional indications for dialysis

⸻

Cefepime and Dialysis

Hemodialysis can substantially enhance cefepime elimination.

In selected patients with severe cefepime neurotoxicity and markedly impaired renal clearance, dialysis may accelerate reduction of drug exposure.

However, the key first intervention remains discontinuation of cefepime and supportive management.

⸻

Monitoring

Monitoring should match the toxicity.

Significant neurotoxicity

• Mental status
• Seizure activity
• Renal function
• ECG/physiologic monitoring when severely ill

Renal toxicity

• Creatinine
• Electrolytes
• Urine output
• Urinalysis

Anaphylaxis

• Airway
• Oxygenation
• Blood pressure
• Recurrence of symptoms

Coagulopathy

• PT/INR
• Bleeding

⸻

Observation

A universal observation period is inappropriate.

Disposition depends on:

• Drug
• Route
• Amount
• Renal function
• Symptoms
• Allergy manifestations
• Neurologic findings
• Coingestants
• Clinical trajectory

Renal impairment can substantially prolong β-lactam toxicity.

⸻

Admission

Hospitalization may be required for:

• Anaphylaxis
• Persistent hypotension
• Airway compromise
• Severe bronchospasm
• Significant encephalopathy
• Seizure
• Nonconvulsive status epilepticus
• Major electrolyte abnormality
• AKI
• Clinically important coagulopathy
• Severe hematologic reaction

ICU care is appropriate for shock, status epilepticus, respiratory failure, or other severe organ dysfunction.

⸻

Pregnancy and Breastfeeding

The old FDA pregnancy letter categories are obsolete.

Penicillins and cephalosporins are among the most commonly used antibiotics during pregnancy, but treatment should still be individualized according to:

• Specific agent
• Infection
• Maternal condition
• Gestational stage
• Allergy history

Many β-lactams enter breast milk in small amounts. Breastfeeding decisions should be drug-specific rather than based simply on detectable milk transfer.

⸻

Safeguarding

Rigid historical age thresholds for assuming abuse, neglect, or intentional poisoning are inappropriate.

Assess pediatric exposures according to:

• Developmental capability
• Medication access
• Circumstances
• Consistency of history
• Recurrent events
• Broader safeguarding concerns

⸻

Prognosis

Most isolated oral penicillin and cephalosporin overdoses resolve uneventfully.

Severe outcomes are more likely from:

• Anaphylaxis
• Parenteral medication errors
• Severe renal impairment with drug accumulation
• Cefepime-associated neurotoxicity
• Major electrolyte abnormalities
• Severe immune-mediated reactions

⸻

Important Modernization of the Older Source

• Acute oral β-lactam overdose is usually mild and GI-predominant.
• The historical oral threshold of 250 mg/kg should not be treated as a universal toxicity cutoff.
• Allergic reactions are not dose dependent.
• IM epinephrine is first-line for anaphylaxis; the older subcutaneous approach is outdated.
• H1 antihistamines are adjuncts in anaphylaxis and must not delay epinephrine; routine H2 blockade is not central treatment.
• The historical “10% penicillin-cephalosporin cross-allergy” figure substantially overstates overall modern cross-reactivity.
• Cross-reactivity depends heavily on side-chain similarity and the nature of the original allergy.
• Cefepime neurotoxicity is an important modern syndrome, especially with renal impairment.
• β-lactam neurotoxicity can cause encephalopathy, myoclonus, seizures, and nonconvulsive status epilepticus.
• Benzodiazepines are first-line for toxicologic seizures; phenytoin is generally not preferred.
• High amoxicillin exposure can cause crystalluria and crystal nephropathy.
• Selected cephalosporins can cause vitamin K–related coagulopathy, but this is not a universal cephalosporin effect.
• Disulfiram-like reactions are agent-specific rather than a class effect.
• Ceftriaxone can rarely cause severe immune hemolysis.
• Flu-like aminopenicillin rashes do not automatically prove true IgE-mediated penicillin allergy.
• Ipecac and routine gastric lavage are obsolete.
• Trendelenburg and dopamine-first shock management are outdated.
• Some β-lactams are dialyzable; dialysis may be particularly useful in selected severe accumulation with renal failure, including serious cefepime neurotoxicity.
• Fixed observation periods should be replaced by agent-, renal-function-, symptom-, and trajectory-based assessment.
• Historical FDA pregnancy categories are obsolete.

Key Points

• Most acute oral penicillin/cephalosporin overdoses are mild.
• Anaphylaxis can occur after very small exposures and is treated first with IM epinephrine.
• Renal impairment greatly increases the risk of β-lactam neurotoxicity.
• Cefepime → encephalopathy, myoclonus, seizures, and nonconvulsive status epilepticus.
• Amoxicillin → crystal nephropathy after sufficiently high exposure.
• Selected cephalosporins can cause coagulopathy, while ceftriaxone can rarely cause immune hemolysis.
• Penicillin-cephalosporin cross-reactivity is much lower and more structurally specific than the historical 10% rule suggests.
• There is no specific antidote.
• Management is primarily supportive, complication-directed, and guided by renal function.

Toxicology – Miscellaneous Antimicrobials

Core Concept

This older grouping combines several unrelated antimicrobial classes, so there is no single toxidrome. The clinically useful approach is to consider each drug separately.

Major agents include:

• Clindamycin and lincomycin
• Chloramphenicol
• Fluoroquinolones — ciprofloxacin, levofloxacin, moxifloxacin, ofloxacin and others
• Vancomycin

Most isolated oral overdoses cause relatively mild GI symptoms. Important toxicity more often occurs from therapeutic exposure, drug interactions, excessive parenteral administration, or impaired clearance.

Characteristic problems are:

• Clindamycin → diarrhea and C. difficile infection
• Chloramphenicol → bone-marrow toxicity; neonatal gray syndrome
• Fluoroquinolones → CNS effects, dysglycemia, QT effects, tendinopathy and peripheral neuropathy
• Vancomycin → nephrotoxicity and infusion reaction

There is no universal antidote.

1. Clindamycin and Lincomycin

Clindamycin is a lincosamide antibiotic that inhibits bacterial protein synthesis through binding to the 50S ribosomal subunit.

Acute oral overdose is generally mild.

Possible effects include:

• Nausea
• Vomiting
• Abdominal discomfort
• Diarrhea

Severe toxicity is uncommon after an isolated ingestion.

Clindamycin and C. difficile

The most clinically important complication is disruption of normal intestinal flora followed by Clostridioides difficile infection (CDI).

This may develop:

• During therapy
• Shortly after therapy
• Even weeks after antibiotic exposure

Symptoms can include:

• Watery diarrhea
• Abdominal pain
• Fever
• Leukocytosis

Severe disease may progress to:

• Ileus
• Toxic megacolon
• Sepsis
• Shock

Modern CDI Diagnosis

Testing should be performed in an appropriate symptomatic patient rather than indiscriminately screening asymptomatic individuals.

Modern testing may involve:

• Stool toxin assays
• NAAT/PCR-based testing
• Multistep diagnostic algorithms

The historical use of routine stool occult blood testing, barium enema, or proctosigmoidoscopy is no longer the standard diagnostic approach.

Modern CDI Treatment

The old statement that antibiotic-associated colitis is simply treated with oral vancomycin needs refinement.

Modern treatment depends on:

• Severity
• Initial vs recurrent infection
• Patient risk factors
• Current infectious-disease guidelines

Fidaxomicin or oral vancomycin are commonly used depending on the clinical setting.

Antimotility drugs are generally avoided in severe or fulminant CDI, particularly when ileus or toxic megacolon is a concern.

Clindamycin – Other Toxicity

Less common effects include:

• Rash
• Hypersensitivity
• Hepatic injury
• Cytopenias
• Rare renal injury

Rapid IV administration has historically been associated with severe cardiovascular reactions, including:

• Hypotension
• Dysrhythmia
• Cardiovascular collapse

These are administration-related events rather than the usual presentation of oral overdose.

2. Chloramphenicol

Chloramphenicol inhibits bacterial protein synthesis at the 50S ribosomal subunit.

Systemic use is now limited in many settings because of serious hematologic toxicity.

The two major toxicologic concepts are:

1. Dose-related reversible bone-marrow suppression
2. Rare idiosyncratic aplastic anemia

These are distinct phenomena.

Dose-Related Bone-Marrow Suppression

High systemic exposure can suppress marrow function.

Possible findings include:

• Anemia
• Leukopenia
• Thrombocytopenia
• Pancytopenia

This form is generally related to dose/exposure and is usually reversible after discontinuation.

Idiosyncratic Aplastic Anemia

A separate and much more concerning reaction is rare aplastic anemia.

Important features:

• Not reliably dose dependent
• Can appear after therapy has stopped
• May be irreversible
• Can be fatal

This toxicity cannot be predicted simply from a chloramphenicol serum concentration.

Chloramphenicol – Gray Baby Syndrome

Neonates have limited capacity to metabolize and eliminate chloramphenicol.

Excessive systemic exposure can therefore produce gray baby syndrome.

Manifestations may include:

• Poor feeding
• Vomiting
• Abdominal distension
• Hypothermia
• Irregular respiration
• Cyanotic or gray discoloration
• Metabolic acidosis
• Hypotension
• Cardiovascular collapse

This is principally a neonatal pharmacokinetic toxicity rather than the typical manifestation of overdose in older children or adults.

Why Neonates Are Vulnerable

Neonates, especially premature infants, have immature:

• Hepatic glucuronidation
• Renal elimination

Therefore:

Reduced clearance → chloramphenicol accumulation → mitochondrial/cardiovascular toxicity

The historical term “gray baby syndrome” should not be generalized to toddlers.

Chloramphenicol Neurologic Toxicity

Prolonged exposure can rarely produce:

• Peripheral neuropathy
• Optic neuropathy
• Visual impairment

The old recommendation to treat chloramphenicol optic neuritis simply with large doses of B vitamins is not an established antidotal strategy.

The essential intervention is recognition and discontinuation of the offending drug, followed by ophthalmologic/neurologic assessment.

Chloramphenicol Concentrations

Serum concentrations can be useful during systemic therapy or suspected major parenteral dosing error.

However, a single historical threshold should not be treated as a universal predictor of toxicity.

Interpret concentrations according to:

• Age
• Dose
• Timing
• Hepatic function
• Renal function
• Clinical condition

3. Fluoroquinolones

Important modern fluoroquinolones include:

• Ciprofloxacin
• Levofloxacin
• Moxifloxacin
• Ofloxacin

Several agents listed in older references are now rarely used or unavailable in many countries.

Fluoroquinolones inhibit bacterial:

• DNA gyrase
• Topoisomerase IV

Acute overdose is usually mild, but this class has several important therapeutic adverse effects.

Fluoroquinolone GI Effects

Common effects include:

• Nausea
• Vomiting
• Abdominal discomfort
• Diarrhea

Antibiotic-associated diarrhea and CDI are also possible.

Fluoroquinolone CNS Toxicity

Neurologic and psychiatric effects can include:

• Headache
• Dizziness
• Insomnia
• Agitation
• Confusion
• Hallucinations
• Tremor
• Rare seizures

Risk may be increased by:

• Older age
• Renal impairment
• CNS disease
• High exposure
• Other medications that lower seizure threshold

Fluoroquinolone Seizures

If a toxicologic seizure occurs:

Benzodiazepines are first-line.

Persistent seizures are managed using standard toxicologic status-epilepticus principles.

Phenytoin is generally not preferred as the routine next treatment for medication-induced seizures.

Fluoroquinolone QT Prolongation

Some fluoroquinolones can delay cardiac repolarization.

The degree varies considerably by agent.

Moxifloxacin has particularly recognized QT-prolonging potential.

Risk increases with:

• Congenital long-QT syndrome
• Hypokalemia
• Hypomagnesemia
• Bradycardia
• Structural cardiac disease
• Other QT-prolonging medications

Torsades

For clinically important QT prolongation or torsades:

• Stop QT-prolonging medications
• Correct potassium
• Correct magnesium
• Give IV magnesium for torsades
• Use electrical treatment when unstable

Recurrent pause-dependent torsades may require selected heart-rate acceleration.

Fluoroquinolone Dysglycemia

Fluoroquinolones can disturb glucose regulation.

Both:

• Hypoglycemia
• Hyperglycemia

have been reported.

Risk is particularly relevant in patients with diabetes or those receiving glucose-lowering medication.

Therefore, altered mental status during fluoroquinolone treatment should include a bedside glucose check.

Tendinopathy and Tendon Rupture

A major modern safety issue is:

• Tendinitis
• Tendon degeneration
• Tendon rupture

The Achilles tendon is commonly involved, although other tendons can be affected.

Risk increases with factors such as:

• Older age
• Corticosteroid treatment
• Transplant status
• Renal dysfunction

This is primarily an adverse effect of therapeutic exposure rather than acute overdose.

Peripheral Neuropathy

Fluoroquinolones can rarely cause peripheral nerve injury.

Symptoms may include:

• Burning pain
• Tingling
• Numbness
• Altered sensation
• Weakness

Symptoms can occasionally persist after the drug has been stopped.

Other Important Fluoroquinolone Adverse Effects

Depending on the individual patient and agent, recognized concerns include:

• Photosensitivity
• Hepatic injury
• Renal injury/crystalluria with selected agents
• Severe hypersensitivity
• C. difficile infection
• Exacerbation of myasthenia gravis

Certain patients also require careful assessment of vascular/aortic risk during therapeutic prescribing.

These complications should not be interpreted as the expected findings after a single accidental ingestion.

Fluoroquinolones in Children

The historical blanket statement that fluoroquinolones must be avoided in everyone aged 17 years or younger is outdated.

They are not universally contraindicated in children.

Pediatric use may be appropriate for selected infections when:

• The organism or disease warrants therapy
• Suitable alternatives are unavailable
• Benefits outweigh musculoskeletal and other risks

Modern prescribing is indication-specific.

Fluoroquinolone Drug Interactions

Ciprofloxacin is an important inhibitor of CYP1A2.

It can increase concentrations of certain medications, particularly:

• Theophylline
• Caffeine
• Some other CYP1A2 substrates

Clinically important theophylline accumulation may cause:

• Vomiting
• Tachycardia
• Tremor
• Agitation
• Seizures
• Dysrhythmias

This should be recognized as an interaction-mediated toxicity.

Chelation in the GI Tract

Oral fluoroquinolone absorption can be substantially reduced by multivalent cations such as:

• Aluminum
• Magnesium
• Calcium
• Iron

This is an important therapeutic interaction but is not a treatment strategy for overdose.

4. Vancomycin

Vancomycin is a glycopeptide antibiotic used for serious gram-positive infections, including many infections caused by resistant organisms.

Its major toxicologic concerns are:

• Nephrotoxicity
• Infusion-related reaction
• Less commonly hematologic or auditory effects

Vancomycin Nephrotoxicity

Vancomycin-associated AKI is clinically important.

Risk increases with:

• High systemic exposure
• Prolonged therapy
• Critical illness
• Preexisting renal dysfunction
• Other nephrotoxic medications

Renal function should be monitored during significant systemic treatment.

Modern Vancomycin Monitoring

Older practice often focused heavily on trough concentrations.

For serious systemic infections, modern therapeutic monitoring increasingly uses AUC-guided exposure assessment rather than relying solely on a trough concentration.

The objective is to balance:

Adequate antimicrobial exposure ↔ reduced nephrotoxicity

This applies to therapeutic monitoring rather than routine evaluation of a small accidental ingestion.

Vancomycin Infusion Reaction

The historical term “red man syndrome” is increasingly replaced by:

Vancomycin infusion reaction

It is caused by non-IgE-mediated histamine release, usually associated with excessively rapid IV administration.

Manifestations include:

• Flushing
• Erythema
• Pruritus
• Warmth
• Upper-body rash
• Occasionally hypotension

Vancomycin Infusion Reaction vs Anaphylaxis

These are not the same process.

Vancomycin infusion reaction

Usually rate-related histamine release.

Anaphylaxis

IgE-mediated or otherwise mast-cell-mediated systemic hypersensitivity with potentially:

• Airway edema
• Bronchospasm
• Hypotension
• Generalized urticaria

True anaphylaxis requires standard emergency management with epinephrine as first-line therapy.

Management of Vancomycin Infusion Reaction

Management generally involves:

• Stop or slow the infusion
• Assess airway and hemodynamics
• Symptomatic antihistamine therapy when appropriate
• Resume more slowly if clinically necessary after symptoms resolve

Severe hypotension requires standard circulatory support.

Vancomycin Ototoxicity

Ototoxicity has historically been associated with vancomycin, but clinically important isolated vancomycin-induced hearing toxicity appears much less common than older literature suggested.

Risk may be greater with:

• Excessive exposure
• Other ototoxic drugs
• Preexisting hearing impairment

New tinnitus or hearing loss warrants evaluation.

Vancomycin Hematologic Effects

Prolonged exposure may rarely cause:

• Neutropenia
• Thrombocytopenia
• Immune-mediated cytopenias

These are generally therapeutic adverse reactions rather than acute overdose findings.

Oral Vancomycin

Oral vancomycin normally has minimal systemic absorption.

Therefore, its toxicity profile differs substantially from IV vancomycin.

Systemic absorption may increase in selected patients with:

• Severe intestinal inflammation
• Renal dysfunction
• Prolonged/high enteral exposure

This distinction is important when evaluating an exposure.

Diagnosis

Always identify:

• Exact antimicrobial
• Route
• Formulation
• Amount
• Timing
• Acute vs prolonged exposure
• Renal/hepatic function
• Coingestants
• Interacting medications

Because these drugs are unrelated pharmacologically, identifying the specific antibiotic is essential.

Laboratory Evaluation

Testing should be drug- and symptom-specific.

Chloramphenicol

Consider:

• CBC
• Electrolytes
• Renal function
• Acid–base assessment in severe toxicity
• Serum concentration when clinically appropriate

Clindamycin

With significant illness consider:

• CBC
• Electrolytes
• Renal/liver function
• Appropriate CDI testing for clinically significant diarrhea

Fluoroquinolones

Consider:

• Glucose
• Electrolytes
• Renal function
• ECG when QT risk exists
• Liver tests when indicated

Vancomycin

Consider:

• Creatinine
• Renal function trend
• Drug exposure monitoring during systemic therapy
• CBC when prolonged therapy or cytopenia is suspected

GI Decontamination

Do not induce vomiting.

Ipecac is obsolete.

Routine gastric lavage is also obsolete.

Activated charcoal may occasionally be considered following a substantial recent ingestion when:

• The agent is adsorbable
• The airway is safe
• Aspiration risk is acceptable
• The expected benefit justifies treatment

Most minor antibiotic ingestions do not require GI decontamination.

Hypotension

Significant hypotension should prompt assessment for:

• Volume depletion
• Infusion reaction
• Anaphylaxis
• Dysrhythmia
• Sepsis
• Coingestants

Appropriate isotonic crystalloid can be used when indicated.

Persistent vasodilatory shock generally favors norepinephrine rather than routine dopamine-first therapy.

Trendelenburg positioning is outdated.

Enhanced Elimination

There is no universal extracorporeal strategy for this group.

Dialysis usefulness depends on the individual antimicrobial’s:

• Protein binding
• Volume of distribution
• Molecular characteristics
• Renal clearance

It should therefore not be summarized simply as “dialysis works” or “dialysis does not work” for miscellaneous antibiotics.

Renal replacement therapy may also be required for conventional indications arising from severe AKI.

No Universal Antidote

There is no specific antidote for:

• Clindamycin
• Chloramphenicol
• Fluoroquinolones
• Vancomycin

Treatment is predominantly:

Stop exposure + supportive care + treat the specific complication

Observation

A fixed observation period is inappropriate for this diverse group.

Disposition depends on:

• Exact antibiotic
• Route
• Amount
• Symptoms
• ECG
• Renal/hepatic function
• Drug interactions
• Acute vs cumulative exposure
• Clinical trajectory

Some important adverse effects, such as aplastic anemia, tendinopathy, peripheral neuropathy, or CDI, cannot be excluded by a few hours of ED observation.

Admission

Hospitalization may be appropriate for:

• Persistent severe vomiting/dehydration
• Significant altered mental status
• Seizure
• Important QT prolongation or dysrhythmia
• Severe hypoglycemia
• Significant AKI
• Severe hepatic injury
• Gray baby syndrome
• Major infusion reaction
• Anaphylaxis
• Severe CDI
• Respiratory compromise

ICU care is appropriate for shock, status epilepticus, malignant dysrhythmia, respiratory failure, or severe neonatal chloramphenicol toxicity.

Pregnancy and Breastfeeding

The historical FDA pregnancy letter categories are obsolete.

Antimicrobial selection during pregnancy or breastfeeding should consider:

• Specific drug
• Infection severity
• Maternal condition
• Gestational/infant age
• Drug transfer
• Available alternatives
• Consequences of untreated infection

The historical blanket statement that fluoroquinolones must always be avoided during breastfeeding is too broad; decisions should be drug- and situation-specific using current lactation guidance.

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional poisoning are inappropriate.

Pediatric exposures should instead be evaluated according to:

• Developmental capability
• Medication accessibility
• Exposure circumstances
• Consistency of history
• Recurrent unexplained events
• Broader safeguarding concerns

Prognosis

Most isolated acute oral exposures have a favorable outcome.

However, important exceptions involve:

Chloramphenicol

• Severe neonatal accumulation
• Aplastic anemia

Clindamycin

• Severe C. difficile infection

Fluoroquinolones

• Severe CNS toxicity
• QT-related dysrhythmia
• Dysglycemia
• Persistent tendon or peripheral nerve complications

Vancomycin

• Significant AKI
• Severe infusion reaction or true anaphylaxis

Important Modernization of the Older Source

• “Miscellaneous antimicrobials” contains pharmacologically unrelated drugs and should be approached agent by agent.
• Clindamycin is strongly associated with C. difficile infection, which can occur during or after therapy.
• Modern CDI diagnosis relies on appropriate stool testing algorithms rather than routine occult blood testing, barium studies, or proctosigmoidoscopy.
• Modern CDI treatment commonly involves fidaxomicin or oral vancomycin, depending on the clinical scenario.
• Chloramphenicol causes both dose-related reversible marrow suppression and a separate rare idiosyncratic aplastic anemia.
• Gray baby syndrome is primarily a toxicity of neonates, especially premature infants, because of immature drug clearance.
• B vitamins are not an established antidote for chloramphenicol optic neuropathy.
• Fluoroquinolones can cause CNS effects, dysglycemia, QT prolongation, tendinopathy/tendon rupture, peripheral neuropathy, and exacerbation of myasthenia gravis.
• Fluoroquinolones are not absolutely prohibited in all children; selected pediatric indications exist.
• Ciprofloxacin can cause clinically important CYP1A2 interactions, particularly with theophylline.
• Vancomycin toxicity centers mainly on AKI and infusion-related reactions.
• “Red man syndrome” is better termed vancomycin infusion reaction.
• Vancomycin infusion reaction is not synonymous with anaphylaxis.
• Modern systemic vancomycin monitoring increasingly emphasizes AUC-guided exposure rather than trough concentration alone.
• Oral vancomycin usually has little systemic absorption.
• Ipecac and routine gastric lavage are obsolete.
• Trendelenburg and routine dopamine-first shock therapy are outdated.
• There is no universal observation period or extracorporeal treatment strategy for this diverse group.
• Historical FDA pregnancy categories are obsolete.

Key Points

• Clindamycin → GI effects and C. difficile infection.
• Chloramphenicol → reversible dose-related marrow suppression + rare idiosyncratic aplastic anemia + neonatal gray syndrome.
• Fluoroquinolones → CNS toxicity, dysglycemia, QT effects, tendinopathy, and peripheral neuropathy.
• Vancomycin → nephrotoxicity and rate-related infusion reaction.
• Severe acute overdose is uncommon with most of these antibiotics.
• Always distinguish acute overdose from adverse effects arising during prolonged therapeutic use.
• Drug interactions and renal dysfunction can substantially alter toxicity.
• There is no single antidote for this group.
• Management is primarily agent-specific supportive care and treatment of complications.

Toxicology – Macrolide Antibiotics

Core Concept

Macrolides are antimicrobial agents used for a variety of bacterial infections. Important modern examples include:

• Azithromycin
• Clarithromycin
• Erythromycin

Older agents such as dirithromycin and troleandomycin are now rarely used or unavailable in many regions.

Isolated acute overdose is usually mild and predominantly gastrointestinal. More important toxicity often occurs during therapeutic use because of:

• QT prolongation and ventricular dysrhythmia
• Drug–drug interactions
• Hepatotoxicity
• Ototoxicity
• Exacerbation of myasthenia gravis

There is no specific antidote.

Mechanism

Macrolides inhibit bacterial protein synthesis by binding primarily to the 50S ribosomal subunit.

Toxic effects are not simply an extension of this antimicrobial mechanism.

Clinically important adverse effects involve:

• GI motility
• Cardiac repolarization
• Hepatic metabolism
• Hearing
• Neuromuscular transmission

Acute Overdose

Most isolated acute macrolide overdoses cause:

• Nausea
• Vomiting
• Abdominal pain
• Diarrhea

Severe poisoning from a single ingestion is uncommon.

Risk assessment should nevertheless consider:

• Exact macrolide
• Amount
• Symptoms
• QT-risk factors
• Electrolyte abnormalities
• Coingestants
• Drug interactions
• Underlying cardiac disease

1. Gastrointestinal Toxicity

GI effects are the most common manifestations.

Possible symptoms include:

• Nausea
• Vomiting
• Abdominal cramping
• Diarrhea

Erythromycin is particularly associated with GI effects because it can stimulate motilin receptors, increasing gastrointestinal motility.

Large fluid losses can occasionally contribute to:

• Dehydration
• Tachycardia
• Hypotension
• Electrolyte abnormalities

2. Cardiotoxicity

Several macrolides can interfere with cardiac repolarization.

The major concern is:

Potassium-channel effects → delayed ventricular repolarization → QT prolongation → torsades de pointes

This is much more important clinically than the older generic description of “ventricular dysrhythmias.”

QT Prolongation

Risk varies among individual macrolides.

Erythromycin and clarithromycin have well-recognized QT-prolonging potential.

Azithromycin can also affect cardiac repolarization, although its interaction profile differs because it has much less CYP3A4 inhibition than erythromycin or clarithromycin.

Risk Factors for Torsades

Risk increases with:

• Baseline prolonged QT
• Congenital long-QT syndrome
• Hypokalemia
• Hypomagnesemia
• Bradycardia
• Structural heart disease
• Older age
• Other QT-prolonging medications
• High systemic exposure
• Drug interactions that increase macrolide concentrations

The presence of multiple risk factors is often more important than the antibiotic alone.

Torsades de Pointes

If macrolide-associated torsades occurs:

• Stop QT-prolonging drugs
• Correct potassium
• Correct magnesium
• Correct other relevant electrolyte abnormalities
• Give IV magnesium
• Treat unstable ventricular dysrhythmia electrically

Recurrent pause-dependent torsades may require heart-rate acceleration, such as selected overdrive pacing.

Avoid adding unnecessary QT-prolonging antiarrhythmics.

ECG Assessment

Obtain an ECG when there is:

• Syncope
• Palpitations
• Significant overdose
• Known long-QT syndrome
• Significant electrolyte disturbance
• Concomitant QT-prolonging drugs
• Cardiovascular instability

Evaluate:

• Rhythm
• Heart rate
• QRS
• QT/QTc
• Ventricular ectopy

Routine prolonged monitoring is unnecessary after every minor asymptomatic ingestion.

3. Drug Interactions

Drug interactions are one of the most clinically important aspects of macrolide toxicity.

However, the older statement that all macrolides broadly inhibit hepatic metabolism is too simplistic.

Erythromycin and clarithromycin

Can significantly inhibit CYP3A4 and alter concentrations of susceptible medications.

Azithromycin

Has substantially less CYP3A4 inhibition and therefore generally causes fewer metabolism-based interactions.

Clinically Important Interactions

Depending on the specific macrolide, interactions may involve:

• Certain statins
• Some calcium-channel blockers
• Calcineurin inhibitors
• Certain benzodiazepines
• Some antiarrhythmics
• Warfarin and other anticoagulant-related therapies
• Digoxin
• Other QT-prolonging medications

The exact interaction must be checked for the individual macrolide rather than assumed to be a class effect.

Macrolides and Statins

CYP3A4-inhibiting macrolides can increase concentrations of susceptible statins.

This can increase the risk of:

• Myopathy
• Rhabdomyolysis
• Acute kidney injury secondary to severe muscle injury

Azithromycin generally has a lower interaction potential than clarithromycin or erythromycin.

Macrolides and Calcium-Channel Blockers

Some macrolides can increase exposure to CYP3A4-metabolized calcium-channel blockers.

Potential consequences include:

• Hypotension
• Bradycardia
• Acute kidney injury secondary to hemodynamic compromise

This is primarily an interaction problem rather than direct macrolide poisoning.

Macrolides and Digoxin

Some macrolides may increase digoxin exposure through mechanisms including alterations in transport and intestinal flora.

If digoxin toxicity develops, manifestations may include:

• Nausea
• Bradyarrhythmia
• AV block
• Ventricular dysrhythmia
• Hyperkalemia in severe acute poisoning

The resulting syndrome should be treated as digoxin toxicity, not simply as macrolide overdose.

4. Hepatotoxicity

Macrolides can cause liver injury.

Possible manifestations include:

• Transaminase elevation
• Cholestatic hepatitis
• Jaundice
• Rare severe hepatic dysfunction

Certain erythromycin formulations, historically especially erythromycin estolate, have been strongly associated with cholestatic liver injury.

Hepatic Evaluation

Consider:

• AST/ALT
• Bilirubin
• Alkaline phosphatase
• Coagulation studies in severe liver dysfunction

Testing is most relevant when the patient develops:

• Jaundice
• Pruritus
• Persistent vomiting
• Right-upper-quadrant symptoms
• Unexplained systemic illness

Routine liver testing is unnecessary after every small acute ingestion.

5. Ototoxicity

Macrolides can occasionally produce sensorineural hearing impairment, particularly with high systemic exposure or prolonged treatment.

Possible symptoms include:

• Tinnitus
• Reduced hearing
• Hearing distortion

Risk may increase with:

• High doses
• Renal or hepatic dysfunction
• Prolonged therapy
• Other ototoxic medications

Macrolide-associated hearing impairment is often reversible after withdrawal, although persistent deficits have occasionally been reported.

6. Myasthenia Gravis

Macrolides may impair neuromuscular transmission and can exacerbate myasthenia gravis.

Possible manifestations include:

• Ptosis
• Diplopia
• Dysphagia
• Dysarthria
• Generalized weakness
• Respiratory muscle weakness

A patient with myasthenia gravis who develops worsening weakness after starting a macrolide requires prompt assessment.

Severe respiratory weakness may require ventilatory support.

7. Infusion-Related Effects

IV erythromycin can cause:

• Local pain
• Venous irritation
• Thrombophlebitis

This is mainly a complication of parenteral therapeutic administration rather than oral overdose.

Antibiotic-Associated Diarrhea

Macrolides can alter intestinal flora.

Diarrhea during or following antibiotic treatment may simply be medication related, but persistent or severe diarrhea should raise concern for Clostridioides difficile infection.

This is an antibiotic complication rather than a direct overdose effect.

Diagnosis

Diagnosis requires identification of:

• Exact macrolide
• Formulation
• Route
• Amount
• Timing
• Symptoms
• Coingestants
• Other medications

A medication review is particularly important because a serious presentation may result from a drug interaction rather than the macrolide concentration alone.

Laboratory Evaluation

No laboratory testing may be necessary after a small, uncomplicated exposure.

For significant illness, consider:

• Glucose
• Electrolytes
• Potassium
• Magnesium
• Creatinine
• Liver tests

Additional testing depends on suspected interactions.

For example:

• CK if rhabdomyolysis is suspected
• Digoxin concentration if digoxin toxicity is suspected
• Coagulation testing when a clinically important anticoagulant interaction is suspected

Serum Macrolide Concentrations

Routine serum erythromycin, clarithromycin, or azithromycin concentrations are not useful in acute poisoning.

Clinical findings, ECG, electrolytes, organ function, and interacting medications are more useful.

Occult Coingestion

Intentional overdose warrants evaluation for clinically important coingestants.

Acetaminophen testing is often appropriate because early toxicity may be asymptomatic.

Other testing should be directed by the history and clinical presentation.

Initial Management

General priorities are:

Airway/breathing → circulation → identify exact macrolide → review interacting medications → ECG when indicated → correct electrolytes → supportive care

Most isolated acute overdoses require only symptomatic treatment.

GI Decontamination

Do not induce vomiting.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a substantial recent ingestion when:

• The exposure is potentially clinically important
• The drug is adsorbable
• The airway is safe
• Aspiration risk is low

Because most isolated macrolide overdoses are relatively benign, charcoal is unnecessary in many cases.

Vomiting and Dehydration

Persistent GI losses should be treated with:

• Appropriate oral or IV fluid replacement
• Correction of electrolyte abnormalities
• Symptomatic care

When selecting an antiemetic, consider whether it also prolongs QT in a patient already at risk for macrolide-associated QT prolongation.

Hypotension

Significant hypotension should prompt evaluation for:

• Severe dehydration
• Dysrhythmia
• Drug interaction
• Anaphylaxis
• Coingestant
• Sepsis or underlying illness

Management includes appropriate isotonic crystalloid and treatment of the underlying cause.

Persistent vasodilatory shock generally favors norepinephrine rather than the historical dopamine-first approach.

Trendelenburg positioning is obsolete.

Anaphylaxis

Although uncommon, immediate hypersensitivity can occur.

For true anaphylaxis:

Epinephrine is first-line therapy.

Airway, breathing, and circulatory support should follow standard anaphylaxis management.

Enhanced Elimination

Hemodialysis and hemoperfusion are not routinely useful for macrolide overdose.

These drugs generally have pharmacokinetic characteristics that limit meaningful extracorporeal removal.

Management remains predominantly supportive.

Monitoring

Monitoring depends on the presentation.

Minor uncomplicated exposure

Usually requires:

• Vital signs
• Symptom assessment

Significant exposure or cardiac risk

Consider:

• Continuous ECG
• Potassium
• Magnesium
• Renal function
• QT trend

Suspected interaction

Monitor the toxicity of the affected interacting drug.

Observation and Disposition

There is no universal observation period for all macrolide exposures.

Disposition depends on:

• Exact drug
• Amount
• Symptoms
• ECG
• Electrolytes
• Drug interactions
• Coingestants
• Clinical trajectory

An asymptomatic minor accidental ingestion generally does not require prolonged monitoring.

Admission

Hospitalization may be appropriate for:

• Persistent severe vomiting/dehydration
• Significant electrolyte disturbance
• Syncope with abnormal ECG
• Marked QT prolongation
• Ventricular dysrhythmia
• Significant hypotension
• Severe hepatic injury
• Severe rhabdomyolysis from a drug interaction
• Myasthenic deterioration
• Respiratory compromise

ICU care is appropriate for torsades, cardiovascular collapse, severe respiratory weakness, or other major organ dysfunction.

Pregnancy

The old FDA pregnancy letter categories are obsolete.

Antibiotic selection during pregnancy should consider:

• Specific macrolide
• Infection being treated
• Gestational stage
• Available alternatives
• Maternal and fetal risks of untreated infection

Erythromycin and azithromycin have substantial clinical experience, while individual macrolides should still be assessed separately.

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional poisoning are outdated.

Pediatric exposures should instead be evaluated according to:

• Developmental capability
• Medication accessibility
• Circumstances of exposure
• Consistency of history
• Recurrent unexplained events
• Broader safeguarding concerns

Prognosis

Most isolated acute macrolide overdoses have a favorable outcome.

Prognosis becomes more concerning when toxicity involves:

• Torsades or other ventricular dysrhythmia
• Severe electrolyte abnormalities
• Major drug interactions
• Significant hepatic injury
• Severe myasthenic weakness
• Complications of prolonged hypoperfusion or hypoxia

Ototoxicity is frequently reversible but should still be formally evaluated when clinically significant.

Important Modernization of the Older Source

• Acute isolated macrolide overdose is usually GI-predominant and relatively benign.
• QT prolongation and torsades are the major direct cardiac concerns.
• Erythromycin and clarithromycin have greater CYP3A4 interaction potential than azithromycin.
• It is inaccurate to treat all macrolides as equally potent inhibitors of hepatic drug metabolism.
• Serious toxicity frequently reflects a drug interaction rather than the antibiotic overdose itself.
• Macrolide–statin interactions can cause myopathy and rhabdomyolysis.
• Macrolide–calcium-channel blocker interactions can contribute to hypotension and AKI.
• Macrolides can exacerbate myasthenia gravis.
• Macrolide-associated hearing loss is usually reversible but can occasionally persist.
• Persistent antibiotic-associated diarrhea should raise consideration of C. difficile infection.
• Routine serum macrolide concentrations are not clinically useful.
• Ipecac and routine gastric lavage are obsolete.
• Activated charcoal is only selectively useful.
• Hemodialysis and hemoperfusion are not routine treatments.
• Trendelenburg and routine dopamine-first shock management are outdated.
• Monitoring and disposition should be based on symptoms, ECG, electrolytes, interactions, and clinical trajectory rather than a fixed observation interval.
• Historical FDA pregnancy letter categories are obsolete.

Key Points

• Macrolide overdose usually causes nausea, vomiting, abdominal pain, and diarrhea.
• Erythromycin and clarithromycin can prolong QT and cause torsades.
• Correct hypokalemia and hypomagnesemia when QT prolongation is present.
• IV magnesium is central to treatment of torsades.
• Erythromycin and clarithromycin can cause important CYP3A4-mediated interactions.
• Azithromycin generally has fewer CYP3A4 interactions but is not completely free of cardiac risk.
• Macrolides may cause cholestatic/hepatic injury, reversible ototoxicity, and worsening of myasthenia gravis.
• There is no specific antidote.
• Treatment is primarily supportive, ECG-directed, and interaction-focused.

Toxicology – Antituberculous Agents

Core Concept

Antituberculous medications have very different toxicity profiles, so poisoning should be approached agent by agent rather than as a single toxidrome.

This section focuses on:

• Ethambutol
• Cycloserine
• Capreomycin
• Para-aminosalicylic acid (PAS)

Isoniazid and rifampin are best considered separately because they have distinctive toxicology.

Modern tuberculosis therapy has also expanded to include agents such as bedaquiline, pretomanid, linezolid, and delamanid, especially in drug-resistant disease.

Major toxicities in this group include:

• Ethambutol → optic neuropathy
• Cycloserine → CNS and psychiatric toxicity, including seizures
• Capreomycin → renal, electrolyte, auditory, and vestibular toxicity
• PAS → GI, hepatic, hematologic, and hypersensitivity reactions

There is no single antidote for the entire group.

1. Ethambutol

Ethambutol inhibits mycobacterial cell-wall synthesis by interfering with arabinosyl transferases involved in arabinogalactan production.

Its most characteristic toxicity is:

Optic neuropathy

This usually develops during therapeutic exposure rather than following a single acute ingestion.

Ethambutol Optic Neuropathy

Clinical manifestations may include:

• Reduced visual acuity
• Blurred vision
• Central or cecocentral visual defects
• Impaired color discrimination
• Reduced contrast sensitivity

Classically, red-green color discrimination may be affected, but color abnormalities are not restricted to one specific pattern.

Risk Factors for Ethambutol Eye Toxicity

Risk increases with:

• Higher exposure
• Longer duration of treatment
• Renal impairment
• Older age
• Preexisting ophthalmic disease

Because ethambutol is substantially cleared by the kidneys, impaired renal function can increase systemic exposure.

Reversibility of Visual Toxicity

Visual function often improves after early recognition and discontinuation, but recovery may be:

• Slow
• Incomplete
• Occasionally poor

Permanent visual impairment can occur.

Therefore, new visual symptoms during ethambutol treatment require prompt assessment.

Ethambutol Monitoring

Patients should be educated to report:

• Blurred vision
• Reduced acuity
• Altered color perception
• New central visual disturbance

Depending on risk and treatment duration, monitoring may include:

• Visual acuity
• Color vision
• Formal ophthalmologic evaluation

Renal function should also be considered because it influences clearance.

Other Ethambutol Effects

Less characteristic adverse effects include:

• GI symptoms
• Rash
• Hyperuricemia
• Peripheral neuropathy
• Rare hematologic abnormalities
• Rare hepatic injury

The older source overemphasizes bone-marrow and liver toxicity relative to ethambutol’s defining clinical problem: optic neuropathy.

2. Cycloserine

Cycloserine is a second-line antituberculous drug that interferes with bacterial cell-wall synthesis.

Its toxicology is dominated by the central nervous system.

Important manifestations include:

• Irritability
• Headache
• Tremor
• Confusion
• Depression
• Anxiety
• Psychosis
• Seizures
• Encephalopathy
• Coma in severe poisoning

Neuropsychiatric toxicity may develop during therapeutic treatment as well as excessive exposure.

Cycloserine – Psychiatric Effects

Cycloserine is particularly notable for psychiatric adverse effects.

Possible manifestations include:

• Mood disturbance
• Anxiety
• Behavioral changes
• Hallucinations
• Psychosis
• Suicidal thoughts or behavior

New psychiatric symptoms during treatment should therefore be taken seriously and assessed clinically rather than automatically attributed to the underlying illness.

Cycloserine and Seizures

Cycloserine can interfere with pathways involving GABA, lowering the seizure threshold.

Risk increases with:

• Excessive systemic concentrations
• Renal impairment
• CNS disease
• Other proconvulsant drugs
• Alcohol use or withdrawal
• Electrolyte disturbances

Cycloserine and Renal Function

Cycloserine is substantially eliminated by the kidneys.

Therefore:

Renal impairment → reduced clearance → accumulation → greater neurotoxicity

Dose adjustment and clinical monitoring are particularly important when kidney function declines.

Cycloserine Concentrations

Unlike many poisoning scenarios, serum cycloserine concentrations can sometimes help evaluate accumulation during therapy.

However, a rigid historical concentration threshold should not replace clinical assessment.

Management should be guided by:

• Neurologic findings
• Renal function
• Exposure history
• Clinical trajectory

Cycloserine and Pyridoxine

Pyridoxine (vitamin B6) supplementation is commonly used during cycloserine therapy to reduce neurologic adverse effects.

Pyridoxine may also be considered as an adjunct in significant cycloserine neurotoxicity.

However, the evidence and role are less definitive than in isoniazid poisoning, where pyridoxine is a central antidotal treatment.

Cycloserine Seizure Treatment

For acute toxicologic seizures:

Benzodiazepines are first-line.

Persistent seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic management for refractory status epilepticus

Pyridoxine can be considered as an adjunct when cycloserine toxicity is strongly suspected.

Physostigmine – Important Correction

The historical recommendation of physostigmine for cycloserine-associated neuromuscular blockade is not standard modern toxicologic management.

Physostigmine should not be treated as a cycloserine antidote.

Severe weakness or respiratory failure is managed primarily with:

• Airway support
• Ventilation
• Correction of contributing abnormalities
• Discontinuation of the causative drug

Hemodialysis and Cycloserine

Cycloserine has pharmacokinetic characteristics that allow extracorporeal removal.

Hemodialysis may therefore be considered in severe poisoning or marked accumulation, particularly when:

• Renal failure is present
• Severe neurologic toxicity persists
• Recurrent seizures occur
• Clearance is substantially impaired

Dialysis decisions should be individualized with toxicology/nephrology input.

3. Capreomycin

Capreomycin is an older injectable antimycobacterial agent historically used particularly for resistant tuberculosis.

Its contemporary use has declined substantially as treatment strategies for drug-resistant TB have changed.

Its toxicity resembles aminoglycoside toxicity in several respects.

Major targets are:

• Kidneys
• Electrolytes
• Cochlear/vestibular system

Capreomycin Nephrotoxicity

Capreomycin can cause renal tubular injury.

Possible findings include:

• Rising creatinine
• Azotemia
• Tubular dysfunction
• Acute kidney injury

Risk increases with:

• Prolonged therapy
• Renal impairment
• Dehydration
• Other nephrotoxic drugs

Capreomycin Electrolyte Disturbances

Renal tubular effects can cause significant electrolyte losses, particularly:

• Hypokalemia
• Hypomagnesemia

Other electrolyte and acid–base disturbances can occur.

These abnormalities may contribute to:

• Weakness
• ECG abnormalities
• Dysrhythmia risk

Capreomycin Ototoxicity

Capreomycin may produce:

• Tinnitus
• Hearing loss
• Vestibular dysfunction
• Disequilibrium
• Vertigo

As with aminoglycosides, ototoxicity can sometimes be persistent or irreversible.

Capreomycin Neuromuscular Effects

Neuromuscular blockade has been reported.

Severe blockade could theoretically produce:

• Weakness
• Hypoventilation
• Respiratory failure

Management is primarily supportive, including mechanical ventilation when necessary.

4. Para-Aminosalicylic Acid – PAS

PAS is an older antituberculous medication now used mainly in selected resistant-TB regimens.

Its adverse-effect profile is dominated by:

• GI intolerance
• Hypersensitivity
• Hepatotoxicity

Acute overdose experience is limited.

PAS Gastrointestinal Toxicity

Common adverse effects include:

• Nausea
• Vomiting
• Abdominal discomfort
• Diarrhea

GI intolerance can become clinically important during prolonged treatment.

PAS Hypersensitivity

Hypersensitivity reactions may produce:

• Fever
• Rash
• Systemic symptoms

More serious immune-mediated effects have occasionally been described, including hepatic or hematologic involvement.

PAS Hepatic Toxicity

PAS may cause:

• Transaminase elevation
• Hepatitis
• Rare clinically significant hepatic dysfunction

Patients developing systemic hypersensitivity symptoms plus hepatic abnormalities require prompt assessment.

PAS Hematologic Effects

Rare abnormalities can include:

• Leukopenia
• Agranulocytosis
• Thrombocytopenia
• Hemolytic anemia

These are primarily complications of therapeutic exposure rather than the expected manifestation of a single acute ingestion.

PAS and Thyroid Function

A useful modern addition is that prolonged PAS therapy can contribute to hypothyroidism, especially when combined with other drugs that impair thyroid function.

This is mainly a chronic-treatment issue rather than acute poisoning.

Acute Oral Overdose

For several of these agents, acute single-ingestion data are limited.

The absence of extensive overdose reports does not mean toxicity is impossible, but many important complications occur through:

Repeated dosing + accumulation + organ dysfunction

rather than immediately after one ingestion.

Diagnosis

Identify the exact antituberculous agent.

Then assess the organ system characteristic of that drug:

Ethambutol → eyes

Cycloserine → CNS/psychiatric system

Capreomycin → kidney/electrolytes/hearing

PAS → GI/liver/hypersensitivity/blood

This agent-specific approach is more useful than treating them as a single toxicologic syndrome.

Laboratory Evaluation

Testing should be directed by the drug and symptoms.

Ethambutol

Consider:

• Renal function
• Ophthalmologic evaluation when visual symptoms occur
• Additional testing based on clinical presentation

Cycloserine

Consider:

• Glucose
• Electrolytes
• Renal function
• Acid–base status after severe seizures
• Drug concentration in selected circumstances

Capreomycin

Consider:

• Creatinine/BUN
• Potassium
• Magnesium
• Calcium
• Bicarbonate
• Other electrolytes
• ECG when significant electrolyte disturbance is present
• Hearing/vestibular assessment when symptomatic

PAS

Consider:

• Liver tests
• CBC when hematologic toxicity is suspected
• Electrolytes/renal function with significant GI losses

ECG

Routine continuous ECG monitoring is not necessary for every minor exposure.

It is appropriate when there is:

• Significant electrolyte abnormality
• Severe systemic illness
• Hypotension
• Altered consciousness
• Significant coingestion
• Dysrhythmia

Occult Coingestion

In an intentional overdose, evaluate for clinically important coingestants.

Acetaminophen testing is often useful because early poisoning can be clinically silent.

Additional testing should be guided by history and presentation rather than routine indiscriminate drug screening.

Initial Management

General priorities are:

Airway/breathing → circulation → identify exact drug → treat seizures → evaluate characteristic target organs → correct metabolic abnormalities

There is no universal antidote for this group.

GI Decontamination

Do not induce vomiting.

Ipecac is obsolete.

Routine gastric lavage is also obsolete.

Activated charcoal may occasionally be considered after a substantial recent ingestion when:

• The substance is adsorbable
• The airway is safe
• Aspiration risk is acceptable
• Expected benefit justifies treatment

Routine decontamination is unnecessary for many minor exposures.

Hypotension

If hypotension develops:

• Assess volume status
• Give appropriate isotonic crystalloid when indicated
• Correct contributing metabolic abnormalities
• Treat anaphylaxis when present
• Use vasopressor support for persistent shock

Norepinephrine is generally favored for persistent vasodilatory shock.

Trendelenburg positioning and automatic dopamine-first therapy are outdated.

Anaphylaxis

Any of these drugs can potentially cause hypersensitivity.

When true anaphylaxis occurs:

Epinephrine is first-line therapy.

Airway, oxygenation, circulation, and additional supportive treatment should follow standard anaphylaxis management.

Renal Injury

For capreomycin-associated renal toxicity:

• Stop further exposure
• Optimize volume status
• Avoid additional nephrotoxins where possible
• Monitor creatinine
• Monitor urine output
• Correct potassium and magnesium abnormalities

Renal replacement therapy is reserved for appropriate clinical indications.

Visual Toxicity

Suspected ethambutol optic neuropathy requires:

• Prompt recognition
• Discontinuation/reassessment of ethambutol therapy
• Ophthalmologic evaluation
• Review of renal function

Do not wait for profound visual loss before investigating symptoms.

Monitoring

Monitoring should match the agent.

Ethambutol

• Vision
• Renal function

Cycloserine

• Mental status
• Psychiatric symptoms
• Seizures
• Renal function

Capreomycin

• Renal function
• Potassium
• Magnesium
• Hearing
• Vestibular symptoms

PAS

• GI tolerance
• Liver function
• CBC when indicated
• Thyroid function during prolonged therapy when clinically appropriate

Observation

The historical universal 4–6-hour observation period is too simplistic.

Disposition depends on:

• Exact drug
• Route
• Amount
• Acute vs cumulative exposure
• Renal function
• Symptoms
• Laboratory abnormalities
• Coingestants
• Clinical trajectory

Several important toxicities—particularly ethambutol optic neuropathy and cumulative capreomycin toxicity—cannot be excluded by a few hours of emergency-department observation.

Admission

Hospitalization may be appropriate for:

• Seizures
• Severe altered mental status
• Psychosis with safety concerns
• Coma
• Respiratory failure
• Significant AKI
• Major electrolyte disturbances
• Severe hypersensitivity/anaphylaxis
• Significant hepatic injury
• Severe coingestion

ICU care is appropriate for refractory seizures, coma, respiratory failure, shock, or other major organ dysfunction.

Pregnancy

The old FDA pregnancy letter categories are obsolete.

Tuberculosis during pregnancy itself poses important maternal and fetal risks, so treatment decisions require balancing:

• Severity and drug susceptibility of TB
• Specific medication
• Maternal condition
• Gestational stage
• Available alternatives

Potential drug toxicity should therefore be considered within the context of maintaining effective tuberculosis treatment.

Pediatric Use – Important Correction

The historical statement that ethambutol, cycloserine, and capreomycin are simply “not recommended for pediatric use” is outdated as a blanket rule.

Modern pediatric TB treatment is based on:

• Drug susceptibility
• Disease severity
• Age
• Ability to monitor toxicity
• Contemporary TB guidelines

Ethambutol, in particular, is used in children when clinically indicated.

Safeguarding

Rigid age cutoffs for assuming neglect, abuse, or intentional poisoning are outdated.

Pediatric exposures should instead be assessed according to:

• Developmental capability
• Medication access
• Exposure circumstances
• Consistency of history
• Recurrent unexplained events
• Broader safeguarding concerns

Prognosis

Ethambutol

Visual toxicity may improve after discontinuation but can be permanent.

Cycloserine

Most acute CNS toxicity is potentially reversible with drug withdrawal and appropriate supportive treatment.

Capreomycin

Renal dysfunction may improve, whereas auditory or vestibular injury may persist.

PAS

GI, hepatic, hypersensitivity, and hematologic effects generally improve after recognition and withdrawal, although severe reactions can require prolonged care.

Important Modernization of the Older Source

• Antituberculous agents have agent-specific toxicities rather than one common poisoning syndrome.
• Ethambutol → optic neuropathy is the defining toxicity.
• Ethambutol toxicity is more likely with prolonged/high exposure and renal impairment.
• Ethambutol is used in modern pediatric TB care when clinically indicated; the historical blanket prohibition is outdated.
• Cycloserine → neuropsychiatric toxicity and seizures.
• Renal impairment increases cycloserine accumulation and CNS toxicity.
• Pyridoxine may be used as an adjunct with cycloserine but does not have the same established antidotal role as in isoniazid poisoning.
• Physostigmine is not a standard cycloserine antidote.
• Hemodialysis can enhance cycloserine elimination in selected severe poisoning.
• Capreomycin → nephrotoxicity + electrolyte wasting + ototoxicity and is now much less prominent in contemporary resistant-TB treatment.
• PAS → GI intolerance + hypersensitivity + hepatic/hematologic effects, with hypothyroidism relevant during chronic therapy.
• Ipecac and routine gastric lavage are obsolete.
• Trendelenburg and routine dopamine-first shock management are outdated.
• Fixed 4–6-hour observation cannot exclude delayed or cumulative toxicities.
• Historical FDA pregnancy letter categories are obsolete.

Key Points

• Ethambutol → optic neuropathy and color/central vision abnormalities.
• Cycloserine → psychiatric changes, tremor, confusion, seizures, and coma.
• Capreomycin → renal injury, hypokalemia/hypomagnesemia, and cochlear/vestibular toxicity.
• PAS → GI, hypersensitivity, hepatic, and hematologic toxicity.
• Renal dysfunction can substantially increase toxicity of renally eliminated TB medications.
• Benzodiazepines are first-line for cycloserine-associated toxicologic seizures.
• Pyridoxine may be considered as an adjunct for cycloserine neurotoxicity.
• Severe cycloserine accumulation may be amenable to hemodialysis.
• New visual symptoms during ethambutol therapy require prompt evaluation.
• There is no single antidote or universal monitoring strategy for this group.

Toxicology – Aminoglycoside Antimicrobials

Core Concept

Aminoglycosides are bactericidal antibiotics used mainly for serious infections caused by susceptible aerobic gram-negative organisms, often as part of combination therapy.

Important agents include:

• Gentamicin
• Tobramycin
• Amikacin
• Streptomycin
• Plazomicin
• Neomycin — mainly topical/oral nonabsorbed use
• Kanamycin — now rarely used in many settings

The major toxicities are:

• Nephrotoxicity
• Ototoxicity
• Rare neuromuscular blockade

Unlike many acute poisonings, clinically important aminoglycoside toxicity usually reflects repeated exposure or impaired clearance, rather than a single isolated dose.

Mechanism of Antimicrobial Action

Aminoglycosides enter susceptible bacteria and bind primarily to the 30S ribosomal subunit.

This disrupts protein synthesis through mechanisms including:

• Interference with initiation
• Misreading of mRNA
• Production of abnormal proteins

Their antibacterial activity is concentration dependent.

Toxicokinetics

Aminoglycosides are:

• Highly water soluble
• Poorly absorbed from the normal GI tract
• Distributed mainly in extracellular fluid
• Minimally metabolized
• Eliminated predominantly by the kidneys

Therefore:

Reduced renal function → decreased clearance → accumulation → increased toxicity

This is fundamental to aminoglycoside toxicology.

Acute vs Cumulative Toxicity

A single accidental dose, even if excessive, often does not produce the characteristic renal or auditory toxicity when baseline renal function is normal.

Greater concern arises with:

• Repeated excessive dosing
• Prolonged therapy
• Renal impairment
• Dehydration
• Critical illness
• Older age
• Concomitant nephrotoxins
• Persistently excessive systemic exposure

Thus, cumulative exposure is generally more informative than a single historical “toxic dose.”

1. Nephrotoxicity

Aminoglycosides accumulate within proximal renal tubular cells.

Intracellular accumulation causes cellular injury and can produce:

Proximal tubular injury → impaired renal function → acute kidney injury

The injury is usually nonoliguric initially, although more severe renal dysfunction can occur.

Clinical Features of Renal Toxicity

Possible findings include:

• Rising serum creatinine
• Reduced GFR
• Tubular dysfunction
• Electrolyte abnormalities

Importantly, renal injury usually develops after several days of exposure, rather than immediately after a single dose.

Reversibility

Aminoglycoside nephrotoxicity is often at least partially reversible after the drug is discontinued because tubular epithelium can recover.

However, severe AKI can require temporary renal replacement therapy.

Risk Factors for Nephrotoxicity

Important risk factors include:

• Preexisting kidney disease
• Prolonged therapy
• Excessive systemic exposure
• Older age
• Dehydration or hypovolemia
• Critical illness
• Sepsis
• Concurrent nephrotoxic medications

Nephrotoxic combinations deserve particular attention.

Other Nephrotoxic Drugs

Potentially important interacting exposures include:

• Vancomycin
• Amphotericin B
• Cisplatin
• Calcineurin inhibitors
• Other nephrotoxic medications

The total clinical context matters more than memorizing a single historical drug combination.

2. Ototoxicity

Aminoglycosides can damage sensory structures of the inner ear.

Toxicity may involve:

Cochlear system

→ hearing impairment

Vestibular system

→ disequilibrium/vertigo

Different aminoglycosides have somewhat different tendencies toward cochlear versus vestibular toxicity.

Cochlear Toxicity

Possible manifestations include:

• Tinnitus
• Reduced hearing
• Difficulty hearing high-frequency sounds
• Progressive sensorineural hearing loss

High-frequency hearing loss may occur before the patient recognizes impairment in ordinary conversation.

Vestibular Toxicity

Possible findings include:

• Dizziness
• Vertigo
• Disequilibrium
• Oscillopsia
• Gait instability

Severe bilateral vestibular injury may cause substantial chronic disability even without dramatic spinning vertigo.

Ototoxicity May Be Permanent

This distinguishes aminoglycoside ototoxicity from much of their renal toxicity.

Renal injury frequently improves after drug withdrawal.

In contrast:

Cochlear or vestibular damage may be irreversible.

Therefore, early recognition is important.

Delayed Ototoxicity

Auditory or vestibular injury may continue to become apparent even after therapy has stopped.

A normal bedside hearing assessment immediately after an exposure does not completely exclude evolving ototoxicity after significant cumulative treatment.

Genetic Susceptibility

Certain mitochondrial genetic variants, particularly involving MT-RNR1, can markedly increase susceptibility to aminoglycoside-associated hearing loss.

In susceptible individuals, significant ototoxicity may occur even with otherwise conventional therapeutic exposure.

This genetic susceptibility was underrecognized in older toxicology references.

3. Neuromuscular Blockade

Aminoglycosides can interfere with neuromuscular transmission.

Mechanisms include impaired presynaptic acetylcholine release and reduced neuromuscular transmission.

Severe toxicity may produce:

• Generalized weakness
• Reduced respiratory muscle strength
• Respiratory depression
• Apnea

This complication is uncommon but potentially life-threatening.

Risk Factors for Neuromuscular Blockade

Risk may increase with:

• High systemic concentrations
• Rapid parenteral administration
• Neuromuscular blocking drugs
• Myasthenia gravis
• Other neuromuscular disorders
• Electrolyte abnormalities
• Anesthesia

Aminoglycosides can potentiate pharmacologic neuromuscular blockade.

Neuromuscular Blockade – Management

The priority is:

Airway protection + ventilation when required + discontinue the offending drug

Modern management should not rely on physostigmine as a specific antidote.

The historical recommendation for physostigmine is not established contemporary treatment for aminoglycoside-induced neuromuscular blockade.

Specialist management may include correction of contributing electrolyte abnormalities and selected pharmacologic measures, but respiratory support is the critical intervention.

4. Oral Exposure

Most aminoglycosides are poorly absorbed from an intact gastrointestinal tract.

Therefore, an isolated accidental oral ingestion usually produces little systemic toxicity.

This is especially relevant to agents such as neomycin.

However, systemic absorption may become more significant when:

• GI mucosa is severely damaged
• Large or prolonged enteral exposure occurs
• Renal function is impaired

Topical Exposure

Topical aminoglycosides generally produce limited systemic absorption.

However, absorption can increase when applied extensively to:

• Large burns
• Open wounds
• Damaged mucosa
• Large body-surface areas

Repeated exposure can also produce contact sensitization, particularly with neomycin.

5. Hypersensitivity

Aminoglycosides may cause allergic reactions.

Manifestations can include:

• Rash
• Contact dermatitis
• Urticaria
• Rare severe immediate hypersensitivity

Neomycin is particularly well recognized as a cause of allergic contact dermatitis.

Therapeutic Drug Monitoring

The older fixed “toxic peak and trough” thresholds should not be treated as universal modern cutoffs.

Aminoglycoside monitoring depends on:

• Specific drug
• Dosing strategy
• Infection
• Renal function
• Duration of therapy
• Local pharmacokinetic protocol

Extended-interval dosing has changed how concentrations are interpreted.

Peak Concentration

Historically, peak concentrations were monitored to assess both efficacy and toxicity.

Modern practice recognizes that aminoglycosides exhibit concentration-dependent bacterial killing, so an appropriately high peak may actually be therapeutically desirable.

Therefore:

A high peak is not automatically synonymous with toxicity.

Interpretation depends on the agent and dosing strategy.

Trough Concentration

Persistent drug accumulation before subsequent doses is more concerning for toxicity.

Elevated trough or delayed clearance may indicate:

• Reduced renal elimination
• Excessive cumulative exposure
• Need for dose/interval adjustment

However, specific targets differ between drugs and treatment protocols.

Extended-Interval Dosing

Many patients now receive larger individual doses at longer intervals rather than traditional multiple-daily dosing.

This approach takes advantage of:

• Concentration-dependent killing
• Post-antibiotic effect
• Periods of very low drug concentration between doses

Consequently, old peak/trough values cannot simply be applied to every modern aminoglycoside regimen.

Diagnosis

Suspect aminoglycoside toxicity in a patient receiving one of these drugs who develops:

• Rising creatinine
• New hearing impairment
• Tinnitus
• Disequilibrium
• Vestibular dysfunction
• Unexpected weakness
• Respiratory compromise

Review:

• Drug
• Dose
• Dosing interval
• Duration
• Renal function
• Concentration data
• Other nephrotoxic/ototoxic drugs

Renal Evaluation

Important assessment includes:

• Serum creatinine
• BUN
• Electrolytes
• Urine output
• Serial renal function

Creatinine clearance/eGFR assists dosing assessment but must be interpreted cautiously during rapidly changing AKI because serum creatinine may lag behind true renal function.

Hearing Assessment

When ototoxicity is suspected, formal assessment may include:

• Audiometry
• High-frequency hearing evaluation
• Vestibular testing when indicated

Patients receiving prolonged high-risk therapy may benefit from baseline and follow-up hearing assessment.

Serum Aminoglycoside Concentrations

Drug concentrations can be clinically useful after:

• Significant parenteral dosing error
• Unexpected accumulation
• Renal impairment
• Prolonged therapy

Unlike many toxicologic drug concentrations, aminoglycoside levels can directly assist pharmacokinetic management.

Interpretation should account for the exact timing of blood sampling relative to the dose.

Initial Management

The general approach is:

Stop further exposure → assess renal function → obtain appropriately timed drug concentrations when useful → assess hearing/vestibular function → provide supportive care

Most single exposures in patients with normal renal function do not require aggressive treatment.

GI Decontamination

Because aminoglycosides are poorly absorbed orally, aggressive GI decontamination is generally unnecessary after an isolated oral exposure.

Do not induce vomiting.

Routine gastric lavage is obsolete.

Activated charcoal is generally of little practical value for most isolated aminoglycoside ingestions and should not be used routinely.

Hydration

Maintain appropriate intravascular volume and renal perfusion.

However, forced fluid administration does not “flush out” aminoglycosides and can cause volume overload.

Fluid therapy should therefore be guided by:

• Volume status
• Renal function
• Urine output
• Hemodynamics

Hypotension

Treat clinically significant hypotension with:

• Appropriate isotonic crystalloid when indicated
• Treatment of the underlying cause
• Vasopressor support if shock persists

Norepinephrine is generally favored for persistent vasodilatory shock.

Trendelenburg positioning and routine dopamine-first therapy are outdated.

Hemodialysis

Aminoglycosides have:

• Relatively low molecular weight
• Low protein binding
• Relatively small volume of distribution

Therefore, they are potentially dialyzable.

However, dialysis is usually unnecessary after a single overdose when renal function is normal because endogenous renal elimination is efficient.

When Dialysis May Become Relevant

Renal replacement therapy may be considered when there is:

• Severe renal failure with markedly impaired elimination
• Significant drug accumulation
• Serious toxicity with prolonged high concentrations
• Conventional renal indications such as severe electrolyte, acid–base, or volume abnormalities

The decision should be individualized with toxicology/nephrology input.

No Specific Antidote

There is no established specific antidote that reverses:

• Aminoglycoside nephrotoxicity
• Cochlear injury
• Vestibular injury

Management centers on preventing further exposure and providing organ support.

Differential Diagnosis – Acute Kidney Injury

Other causes of AKI include:

• Sepsis
• Shock
• Dehydration
• Rhabdomyolysis
• Urinary obstruction
• Other nephrotoxic medications
• Toxic alcohols
• Heavy metals

In critically ill patients, aminoglycosides may be only one of several simultaneous renal insults.

Differential Diagnosis – Hearing/Vestibular Symptoms

Consider:

• Other ototoxic medications
• Ear disease
• Vestibular neuritis
• Ménière disease
• Neurologic disorders
• Infection
• Age-related hearing loss

Other drugs with ototoxic potential can amplify risk.

Drug Interactions – Modern Perspective

The older interaction list should not be interpreted as a collection of absolute contraindications.

The clinically important principles are:

• Other nephrotoxins increase renal risk
• Other ototoxins may increase auditory/vestibular risk
• Neuromuscular blockers can have enhanced effects

Aminoglycosides and certain β-lactam antibiotics can also undergo chemical inactivation if physically mixed under inappropriate conditions, but this does not mean that clinically indicated combination therapy is universally prohibited.

Pregnancy

The historical FDA pregnancy letter categories are obsolete.

Systemic aminoglycoside use during pregnancy requires assessment of:

• Maternal infection severity
• Specific aminoglycoside
• Alternative antibiotics
• Gestational circumstances
• Potential fetal ototoxicity

Serious maternal infection may make aminoglycoside therapy appropriate when benefits outweigh potential fetal risks.

Safeguarding

Rigid historical age cutoffs for assuming neglect, abuse, or intentional poisoning are inappropriate.

Pediatric exposures should instead be evaluated according to:

• Developmental capability
• Medication accessibility
• Exposure circumstances
• Consistency of history
• Recurrent unexplained events
• Broader safeguarding concerns

Monitoring

During significant exposure or therapeutic toxicity, monitor:

• Serum creatinine
• Renal function trend
• Urine output
• Electrolytes
• Appropriately timed aminoglycoside concentrations
• Hearing when indicated
• Vestibular function when symptomatic
• Respiratory status if weakness develops

Renal toxicity may not become apparent immediately, so follow-up should reflect the exposure pattern rather than an arbitrary short observation period.

Disposition

An isolated accidental oral exposure in an asymptomatic patient with normal renal function generally has low systemic toxicity.

Further evaluation or admission may be needed for:

• Significant parenteral dosing error
• Renal impairment
• Rising creatinine
• Persistent excessive drug concentrations
• Hearing loss
• Significant vestibular dysfunction
• Neuromuscular weakness
• Respiratory compromise
• Other serious complications

Prognosis

Renal toxicity

Often improves after discontinuation, although severe cases can require temporary dialysis.

Ototoxicity

May be permanent.

Neuromuscular blockade

Usually resolves as drug concentrations fall if adequate respiratory support is provided.

The most important strategy is prevention through appropriate dosing and renal monitoring.

Important Modernization of the Older Source

• Aminoglycoside toxicity is generally a cumulative exposure problem, not a classic single-dose overdose syndrome.
• The major toxicities remain nephrotoxicity and ototoxicity.
• Nephrotoxicity primarily reflects proximal tubular injury and is often reversible.
• Ototoxicity may involve cochlear or vestibular systems and can be permanent.
• MT-RNR1 mitochondrial variants can greatly increase susceptibility to aminoglycoside hearing loss.
• Aminoglycosides can rarely produce clinically important neuromuscular blockade.
• Physostigmine should not be considered a standard antidote for aminoglycoside neuromuscular toxicity.
• Fixed historical peak/trough “toxic levels” should not be applied indiscriminately to modern extended-interval dosing.
• Appropriately timed serum concentrations remain useful for therapeutic monitoring and significant dosing errors.
• Oral aminoglycosides are poorly absorbed, making most isolated oral overdoses low risk.
• Routine gastric lavage is obsolete, and activated charcoal generally has little role.
• Hemodialysis can remove aminoglycosides but is generally reserved for severe accumulation with impaired renal clearance or other dialysis indications.
• The historical statement that gentamicin/tobramycin should not be combined therapeutically with certain β-lactams is overly broad; physical incompatibility and pharmacokinetic issues should be distinguished from clinically useful combination therapy.
• Trendelenburg and routine dopamine-first shock treatment are outdated.
• Pregnancy should no longer be described using the old FDA letter categories.

Key Points

• Aminoglycosides → kidney + inner-ear toxicity.
• Nephrotoxicity = proximal tubular injury and AKI.
• Ototoxicity = cochlear hearing loss and/or vestibular dysfunction.
• Kidney injury is often reversible; hearing or vestibular damage may not be.
• Toxicity is usually associated with repeated exposure, accumulation, or renal impairment.
• A single accidental oral ingestion usually has low systemic toxicity because GI absorption is poor.
• Renal impairment markedly prolongs elimination.
• Serum concentrations are useful when interpreted according to the specific dosing strategy.
• Rare severe toxicity can cause neuromuscular weakness and respiratory failure.
• There is no specific antidote.
• Management centers on stopping exposure, monitoring renal and auditory function, supportive care, and selected dialysis when clearance is severely impaired.