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Toxicology – Anticholinergic Toxidrome
Common Sources
Anticholinergic toxicity can arise from a wide range of medications and substances, including antihistamines, gastrointestinal and genitourinary antispasmodics, tricyclic antidepressants, antiparkinsonian drugs, skeletal muscle relaxants, antivertigo agents, antipsychotics, and plants such as Jimson weed.
Typical Presentation
A common scenario involves a teenager ingesting Jimson weed seeds for recreational purposes. Within a few hours, the individual may develop abnormal behavior, confusion, and delirium, often appearing to respond to internal stimuli. Physical findings may include dilated pupils, dry lips, rapid heart rate, and absent bowel sounds. Urinary retention is also common and may be significant.
Clinical Features
Key signs and symptoms include mydriasis, dry mucous membranes, tachycardia, hyperthermia, hypertension, decreased or absent bowel sounds, warm flushed skin, urinary retention, and altered mental status ranging from confusion to hallucinations and delirium. Severe cases may involve seizures.
Mechanism of Action
These agents block the effects of acetylcholine at muscarinic receptors within the autonomic nervous system. This affects multiple organ systems, including the brain, heart, glands, and smooth muscle of the gastrointestinal and genitourinary tracts. At higher doses, nicotinic receptor blockade may also occur. Atropine is the classic example of an anticholinergic agent.
Management
Treatment is primarily supportive. This includes intravenous fluids, bladder decompression with a Foley catheter if urinary retention is present, cooling measures for hyperthermia, and benzodiazepines for agitation or seizures. Activated charcoal may be used to reduce further absorption if appropriate. Physostigmine, a reversible acetylcholinesterase inhibitor that crosses the blood–brain barrier, may be used as an antidote in selected cases.
Key Points
Common Sources
Anticholinergic toxicity can arise from a wide range of medications and substances, including antihistamines, gastrointestinal and genitourinary antispasmodics, tricyclic antidepressants, antiparkinsonian drugs, skeletal muscle relaxants, antivertigo agents, antipsychotics, and plants such as Jimson weed.
Typical Presentation
A common scenario involves a teenager ingesting Jimson weed seeds for recreational purposes. Within a few hours, the individual may develop abnormal behavior, confusion, and delirium, often appearing to respond to internal stimuli. Physical findings may include dilated pupils, dry lips, rapid heart rate, and absent bowel sounds. Urinary retention is also common and may be significant.
Clinical Features
Key signs and symptoms include mydriasis, dry mucous membranes, tachycardia, hyperthermia, hypertension, decreased or absent bowel sounds, warm flushed skin, urinary retention, and altered mental status ranging from confusion to hallucinations and delirium. Severe cases may involve seizures.
Mechanism of Action
These agents block the effects of acetylcholine at muscarinic receptors within the autonomic nervous system. This affects multiple organ systems, including the brain, heart, glands, and smooth muscle of the gastrointestinal and genitourinary tracts. At higher doses, nicotinic receptor blockade may also occur. Atropine is the classic example of an anticholinergic agent.
Management
Treatment is primarily supportive. This includes intravenous fluids, bladder decompression with a Foley catheter if urinary retention is present, cooling measures for hyperthermia, and benzodiazepines for agitation or seizures. Activated charcoal may be used to reduce further absorption if appropriate. Physostigmine, a reversible acetylcholinesterase inhibitor that crosses the blood–brain barrier, may be used as an antidote in selected cases.
Key Points
- Activated charcoal should only be administered if bowel function is intact.
- Jimson weed and similar substances are sometimes misused recreationally, especially among adolescents.
- In elderly patients, unexplained confusion and urinary retention should raise suspicion for anticholinergic toxicity, particularly after starting new medications such as antihistamines or cold remedies.
- Anticholinergic drugs should be used cautiously in older adults due to the risk of worsening cognitive impairment.
- Classic description: “dry as a bone, red as a beet, hot as a hare, mad as a hatter, and blind as a bat.”
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Toxicology – Organophosphate Poisoning
Sources
Organophosphates are found in both chemical warfare agents—such as sarin, soman, tabun, and VX—and commonly used agricultural insecticides including diazinon, dichlorvos, malathion, and parathion.
Typical Presentation
A classic case involves accidental ingestion or exposure, often in agricultural settings. Patients may present with altered mental status, pinpoint pupils (miosis), excessive secretions, slow heart rate, bronchorrhea, sweating, and respiratory distress requiring airway support.
Mechanism of Action
Organophosphates inhibit acetylcholinesterase at synapses in both the central and peripheral nervous systems, as well as in red blood cells. This leads to accumulation of acetylcholine. Over time, the enzyme undergoes “aging,” making the inhibition irreversible.
Clinical Features
Muscarinic effects are most prominent and include miosis, bradycardia, excessive salivation, sweating, bronchorrhea, bronchospasm, gastrointestinal symptoms (nausea, vomiting, diarrhea), lacrimation, and urinary incontinence. Central nervous system effects include confusion, lethargy, coma, and seizures. Nicotinic effects include muscle fasciculations and weakness. Severe toxicity may be fatal.
Management
Treatment begins with decontamination and supportive care. Atropine is administered to counteract muscarinic effects, particularly respiratory secretions, starting at 2–5 mg IV in adults (0.05 mg/kg in children) and repeated every 3–5 minutes with dose escalation until improvement is seen. Pralidoxime is used to reverse neuromuscular effects and is given intravenously over 30 minutes (1–2 g in adults, 20–50 mg/kg in children). Benzodiazepines, especially diazepam, are used for seizures, agitation, and muscle spasms. Repeated dosing or continuous infusions may be necessary. Autoinjectors containing atropine and pralidoxime are commonly used in emergency and military settings.
Sources
Organophosphates are found in both chemical warfare agents—such as sarin, soman, tabun, and VX—and commonly used agricultural insecticides including diazinon, dichlorvos, malathion, and parathion.
Typical Presentation
A classic case involves accidental ingestion or exposure, often in agricultural settings. Patients may present with altered mental status, pinpoint pupils (miosis), excessive secretions, slow heart rate, bronchorrhea, sweating, and respiratory distress requiring airway support.
Mechanism of Action
Organophosphates inhibit acetylcholinesterase at synapses in both the central and peripheral nervous systems, as well as in red blood cells. This leads to accumulation of acetylcholine. Over time, the enzyme undergoes “aging,” making the inhibition irreversible.
Clinical Features
Muscarinic effects are most prominent and include miosis, bradycardia, excessive salivation, sweating, bronchorrhea, bronchospasm, gastrointestinal symptoms (nausea, vomiting, diarrhea), lacrimation, and urinary incontinence. Central nervous system effects include confusion, lethargy, coma, and seizures. Nicotinic effects include muscle fasciculations and weakness. Severe toxicity may be fatal.
Management
Treatment begins with decontamination and supportive care. Atropine is administered to counteract muscarinic effects, particularly respiratory secretions, starting at 2–5 mg IV in adults (0.05 mg/kg in children) and repeated every 3–5 minutes with dose escalation until improvement is seen. Pralidoxime is used to reverse neuromuscular effects and is given intravenously over 30 minutes (1–2 g in adults, 20–50 mg/kg in children). Benzodiazepines, especially diazepam, are used for seizures, agitation, and muscle spasms. Repeated dosing or continuous infusions may be necessary. Autoinjectors containing atropine and pralidoxime are commonly used in emergency and military settings.
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Toxicology – Carbamate Poisoning
Sources
Carbamates are commonly found in insecticides such as carbaryl, aldicarb, carbofuran, and methomyl. They are also present in certain medications, including acetylcholinesterase inhibitors used for Alzheimer disease (e.g., rivastigmine) and therapeutic agents like neostigmine and physostigmine.
Typical Presentation
A common scenario involves accidental or intentional ingestion, particularly in children exposed to insecticides. Patients typically present with features of a cholinergic toxidrome, including excessive secretions, altered mental status, and respiratory symptoms.
Mechanism of Action
Carbamates inhibit acetylcholinesterase at synapses in both the central and peripheral nervous systems, as well as in red blood cells. Unlike organophosphates, this inhibition is reversible because carbamates do not cause “aging” of the enzyme, making their toxicity generally less severe.
Clinical Features
Muscarinic symptoms predominate and include miosis, bradycardia, salivation, sweating, bronchorrhea, bronchospasm, nausea, vomiting, diarrhea, lacrimation, and urinary incontinence. Central nervous system effects include confusion, lethargy, coma, and seizures. Nicotinic effects include muscle fasciculations and weakness. Severe cases may lead to death.
Management
Treatment involves prompt decontamination and supportive care. Atropine is administered to control muscarinic symptoms, particularly respiratory secretions, starting at 2–5 mg IV in adults (0.05 mg/kg in children) and repeated every 3–5 minutes with dose escalation until improvement is achieved. Pralidoxime may be used for neuromuscular symptoms, although its role is less critical compared to organophosphate poisoning. Benzodiazepines are indicated for agitation, muscle spasms, and seizures. Autoinjectors containing atropine and pralidoxime are available for emergency use.
Key Points
Sources
Carbamates are commonly found in insecticides such as carbaryl, aldicarb, carbofuran, and methomyl. They are also present in certain medications, including acetylcholinesterase inhibitors used for Alzheimer disease (e.g., rivastigmine) and therapeutic agents like neostigmine and physostigmine.
Typical Presentation
A common scenario involves accidental or intentional ingestion, particularly in children exposed to insecticides. Patients typically present with features of a cholinergic toxidrome, including excessive secretions, altered mental status, and respiratory symptoms.
Mechanism of Action
Carbamates inhibit acetylcholinesterase at synapses in both the central and peripheral nervous systems, as well as in red blood cells. Unlike organophosphates, this inhibition is reversible because carbamates do not cause “aging” of the enzyme, making their toxicity generally less severe.
Clinical Features
Muscarinic symptoms predominate and include miosis, bradycardia, salivation, sweating, bronchorrhea, bronchospasm, nausea, vomiting, diarrhea, lacrimation, and urinary incontinence. Central nervous system effects include confusion, lethargy, coma, and seizures. Nicotinic effects include muscle fasciculations and weakness. Severe cases may lead to death.
Management
Treatment involves prompt decontamination and supportive care. Atropine is administered to control muscarinic symptoms, particularly respiratory secretions, starting at 2–5 mg IV in adults (0.05 mg/kg in children) and repeated every 3–5 minutes with dose escalation until improvement is achieved. Pralidoxime may be used for neuromuscular symptoms, although its role is less critical compared to organophosphate poisoning. Benzodiazepines are indicated for agitation, muscle spasms, and seizures. Autoinjectors containing atropine and pralidoxime are available for emergency use.
Key Points
- Carbamates cause reversible inhibition of acetylcholinesterase and are generally less toxic than organophosphates.
- Central-acting acetylcholinesterase inhibitors such as donepezil and tacrine, used in Alzheimer disease, can produce cholinergic toxicity in overdose.
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Toxicology – Opioid (Opiate) Toxidrome
Sources
Opioid toxicity can result from a wide range of substances, including natural and synthetic narcotics such as morphine, heroin, codeine, oxycodone, hydrocodone, fentanyl, methadone, hydromorphone, buprenorphine, oxymorphone, meperidine, propoxyphene, opium, and kratom. These agents may be taken orally, inhaled, or injected. Many prescription formulations combine opioids with acetaminophen, and fentanyl is also available as a transdermal patch.
Typical Presentation
Patients often present with decreased level of consciousness and respiratory depression. A classic presentation includes somnolence, slow breathing, pinpoint pupils, and evidence of intravenous drug use such as track marks. Administration of naloxone can rapidly reverse symptoms, leading to abrupt awakening.
Clinical Features
Common findings include central nervous system depression, bradypnea, bradycardia, reduced bowel sounds, and miosis. Peripheral vasodilation may result in hypotension and hypothermia. Severe toxicity can lead to respiratory arrest and coma. Complications may include noncardiogenic pulmonary edema and, in certain cases such as methadone use, QT prolongation. Repeated dosing of meperidine may provoke seizures.
Mechanism of Action
Opioids exert their effects by binding to specific opioid receptors in the central nervous system and gastrointestinal tract, leading to decreased neuronal excitability and slowed physiological functions.
Management
Treatment is primarily supportive, with airway and breathing support as needed. Naloxone is the antidote and should be administered in small, titrated doses (0.4–2 mg in adults, 0.1 mg/kg in children) every 1–2 minutes until adequate ventilation is restored. Care should be taken to avoid precipitating acute withdrawal. For long-acting opioids, a continuous naloxone infusion (approximately two-thirds of the effective reversal dose per hour) may be required. Whole bowel irrigation may be considered in cases of ingestion of sustained-release formulations or transdermal patches.
Key Points
- Naloxone has a shorter duration of action than many opioids, so repeated dosing or infusion may be necessary.
- Prolonged unconsciousness can lead to complications such as rhabdomyolysis.
- Some opioids, such as propoxyphene, may cause cardiac conduction abnormalities and seizures.
- Many opioid combination products contain acetaminophen, increasing the risk of combined toxicity.
- Transdermal systems and “abuse-deterrent” formulations may still be misused through extraction methods.
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Toxicology – Sedative–Hypnotic (Hypnosedative) Toxidrome
Sources
This toxidrome is associated with a broad group of central nervous system depressants, including alcohols, anticonvulsants, barbiturates, benzodiazepines, chloral hydrate, gamma-hydroxybutyrate (GHB), phenobarbital, meprobamate, methaqualone, muscle relaxants, tranquilizers, and sedative-hypnotic agents such as zolpidem.
Typical Presentation
Patients often present with decreased level of consciousness, ranging from drowsiness to coma. A common scenario involves combined use of substances (e.g., benzodiazepines with alcohol), leading to enhanced sedative effects. Individuals may appear intoxicated, with slurred speech, poor coordination, and impaired balance.
Clinical Features
Findings resemble alcohol intoxication and include respiratory depression, bradycardia, hypotension, ataxia, slurred speech, lethargy, disinhibition, decreased muscle tone, nystagmus, and progressive central nervous system depression. Severe cases may progress to stupor or coma. Effects are typically dose-dependent and often worsened by coingestion with alcohol. Certain agents such as GHB and methaqualone may lower the seizure threshold, while abrupt withdrawal from chronic use can lead to seizures and may be life-threatening.
Mechanism of Action
Most sedative–hypnotic agents exert their effects by enhancing gamma-aminobutyric acid (GABA) activity in the central nervous system, resulting in generalized neuronal inhibition.
Management
Treatment is primarily supportive, with attention to airway protection and hemodynamic stability. In patients with altered mental status, cervical spine precautions and neuroimaging may be necessary to exclude other causes. Endotracheal intubation should be considered in cases of compromised airway or respiratory depression. Flumazenil may be used cautiously in benzodiazepine-naïve patients, but it is generally avoided in chronic users due to the risk of precipitating severe withdrawal and seizures.
Key Points
- Alkalinization of urine can enhance elimination of certain barbiturates.
- Meprobamate toxicity may be managed with dialysis in severe cases.
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Toxicology – Sources of Sedative–Hypnotic Agents
Sedative–hypnotics are substances that produce calming effects and promote sleep. With repeated use, individuals can develop tolerance, dependence, and addiction. Abrupt discontinuation after prolonged use may result in withdrawal symptoms, and cross-tolerance between agents is common.
Alcohols
Various alcohols—including ethanol, methanol, ethylene glycol, and isopropanol—can produce sedative effects. Methanol and ethylene glycol are particularly dangerous due to toxic metabolite formation, while isopropanol can cause profound central nervous system depression.
Barbiturates
This group includes agents such as phenobarbital, pentobarbital, secobarbital, amobarbital, and butalbital, all of which act as potent central nervous system depressants.
Benzodiazepines
Common examples include diazepam, lorazepam, alprazolam, clonazepam, midazolam, oxazepam, triazolam, chlordiazepoxide, flurazepam, and flunitrazepam. These are widely used for anxiety, sedation, and seizure control.
Chloral Hydrate
Available in both liquid and tablet forms, chloral hydrate can cause significant sedation and may lead to unconsciousness when combined with alcohol. It is also associated with cardiac arrhythmias.
Gamma-Hydroxybutyrate (GHB)
This group includes GHB, gamma-butyrolactone (GBL), and 1,4-butanediol. These substances produce rapid sedation and are sometimes misused recreationally.
Non-Benzodiazepine Sedative-Hypnotics (Sleeping Pills)
Medications such as zolpidem, zaleplon, eszopiclone, and zopiclone are commonly prescribed for insomnia and act on similar pathways as benzodiazepines.
Sedative–hypnotics are substances that produce calming effects and promote sleep. With repeated use, individuals can develop tolerance, dependence, and addiction. Abrupt discontinuation after prolonged use may result in withdrawal symptoms, and cross-tolerance between agents is common.
Alcohols
Various alcohols—including ethanol, methanol, ethylene glycol, and isopropanol—can produce sedative effects. Methanol and ethylene glycol are particularly dangerous due to toxic metabolite formation, while isopropanol can cause profound central nervous system depression.
Barbiturates
This group includes agents such as phenobarbital, pentobarbital, secobarbital, amobarbital, and butalbital, all of which act as potent central nervous system depressants.
Benzodiazepines
Common examples include diazepam, lorazepam, alprazolam, clonazepam, midazolam, oxazepam, triazolam, chlordiazepoxide, flurazepam, and flunitrazepam. These are widely used for anxiety, sedation, and seizure control.
Chloral Hydrate
Available in both liquid and tablet forms, chloral hydrate can cause significant sedation and may lead to unconsciousness when combined with alcohol. It is also associated with cardiac arrhythmias.
Gamma-Hydroxybutyrate (GHB)
This group includes GHB, gamma-butyrolactone (GBL), and 1,4-butanediol. These substances produce rapid sedation and are sometimes misused recreationally.
Non-Benzodiazepine Sedative-Hypnotics (Sleeping Pills)
Medications such as zolpidem, zaleplon, eszopiclone, and zopiclone are commonly prescribed for insomnia and act on similar pathways as benzodiazepines.
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Toxicology – Sympathomimetic Toxidrome
Sources
Sympathomimetic agents are substances that stimulate the sympathetic nervous system by increasing catecholamine activity. They may act directly on receptors (e.g., alpha- or beta-agonists) or indirectly by increasing catecholamine release, blocking reuptake, or inhibiting breakdown. Common examples include cocaine, amphetamines, MDMA, ephedrine, pseudoephedrine, epinephrine, MAO inhibitors, and synthetic stimulants such as “bath salts” (e.g., mephedrone).
Typical Presentation
Patients typically present in an agitated, hyperactive state. A common scenario involves stimulant use followed by symptoms such as chest pain, anxiety, and marked vital sign abnormalities including hypertension, tachycardia, and hyperthermia.
Clinical Features
This toxidrome reflects a “fight-or-flight” response. Key findings include tachycardia, hypertension, hyperthermia, dilated pupils, diaphoresis, hyperreflexia, and preserved bowel sounds. Patients may also exhibit agitation, pressured speech, paranoia, tremors, teeth grinding (bruxism), chest pain, and rhabdomyolysis. Unlike anticholinergic toxicity, patients are typically sweaty rather than dry.
Mechanism of Action
These agents stimulate the autonomic nervous system either by directly activating adrenergic receptors or indirectly by increasing catecholamine availability through enhanced release, decreased reuptake, or reduced metabolism.
Management
Treatment is largely supportive. Intravenous fluids are administered for hydration and to prevent or treat rhabdomyolysis. Benzodiazepines are first-line therapy for agitation, anxiety, and chest pain. Severe hyperthermia requires rapid cooling measures. Hypertension may be managed with benzodiazepines, vasodilators such as sodium nitroprusside, or alpha-blockers like phentolamine.
Key Points
Sources
Sympathomimetic agents are substances that stimulate the sympathetic nervous system by increasing catecholamine activity. They may act directly on receptors (e.g., alpha- or beta-agonists) or indirectly by increasing catecholamine release, blocking reuptake, or inhibiting breakdown. Common examples include cocaine, amphetamines, MDMA, ephedrine, pseudoephedrine, epinephrine, MAO inhibitors, and synthetic stimulants such as “bath salts” (e.g., mephedrone).
Typical Presentation
Patients typically present in an agitated, hyperactive state. A common scenario involves stimulant use followed by symptoms such as chest pain, anxiety, and marked vital sign abnormalities including hypertension, tachycardia, and hyperthermia.
Clinical Features
This toxidrome reflects a “fight-or-flight” response. Key findings include tachycardia, hypertension, hyperthermia, dilated pupils, diaphoresis, hyperreflexia, and preserved bowel sounds. Patients may also exhibit agitation, pressured speech, paranoia, tremors, teeth grinding (bruxism), chest pain, and rhabdomyolysis. Unlike anticholinergic toxicity, patients are typically sweaty rather than dry.
Mechanism of Action
These agents stimulate the autonomic nervous system either by directly activating adrenergic receptors or indirectly by increasing catecholamine availability through enhanced release, decreased reuptake, or reduced metabolism.
Management
Treatment is largely supportive. Intravenous fluids are administered for hydration and to prevent or treat rhabdomyolysis. Benzodiazepines are first-line therapy for agitation, anxiety, and chest pain. Severe hyperthermia requires rapid cooling measures. Hypertension may be managed with benzodiazepines, vasodilators such as sodium nitroprusside, or alpha-blockers like phentolamine.
Key Points
- Beta-blockers are generally avoided due to the risk of unopposed alpha-adrenergic vasoconstriction.
- Stimulant drugs can be easily manufactured or obtained, contributing to their widespread use.
- Sympathomimetics lower the seizure threshold, increasing the risk of seizures.
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Toxicology – Cardiotoxic Drugs
Sodium Channel Blockers (Widened QRS)
Several drugs impair cardiac conduction by blocking sodium channels, leading to QRS widening on ECG. These include antihistamines, antimalarials, tricyclic antidepressants, cocaine, and local anesthetics.
QT Prolonging Agents
Certain medications delay cardiac repolarization, resulting in QT interval prolongation and risk of torsades de pointes. Common examples include antipsychotics, macrolide antibiotics, and methadone.
Beta-Blockers
These agents reduce heart rate and conduction through β-adrenergic blockade, potentially causing bradycardia and varying degrees of heart block in overdose.
Calcium Channel Blockers
By inhibiting calcium influx into cardiac cells, these drugs decrease contractility and conduction, leading to bradycardia and heart block.
Digoxin
Digoxin inhibits the Na⁺/K⁺-ATPase pump, increasing intracellular calcium. Toxicity can result in bradycardia, heart block, and potentially life-threatening ventricular arrhythmias.
Antiarrhythmic Drugs
Antiarrhythmics are categorized based on their electrophysiologic effects:
Chemotherapeutic Agents
Certain cancer treatments are associated with cardiotoxicity:
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Sodium Channel Blockers (Widened QRS)
Several drugs impair cardiac conduction by blocking sodium channels, leading to QRS widening on ECG. These include antihistamines, antimalarials, tricyclic antidepressants, cocaine, and local anesthetics.
QT Prolonging Agents
Certain medications delay cardiac repolarization, resulting in QT interval prolongation and risk of torsades de pointes. Common examples include antipsychotics, macrolide antibiotics, and methadone.
Beta-Blockers
These agents reduce heart rate and conduction through β-adrenergic blockade, potentially causing bradycardia and varying degrees of heart block in overdose.
Calcium Channel Blockers
By inhibiting calcium influx into cardiac cells, these drugs decrease contractility and conduction, leading to bradycardia and heart block.
Digoxin
Digoxin inhibits the Na⁺/K⁺-ATPase pump, increasing intracellular calcium. Toxicity can result in bradycardia, heart block, and potentially life-threatening ventricular arrhythmias.
Antiarrhythmic Drugs
Antiarrhythmics are categorized based on their electrophysiologic effects:
- Class I: Sodium channel blockers (Ia prolong action potential, Ib shorten it, Ic have minimal effect)
- Class II: Beta-blockers
- Class III: Potassium channel blockers (prolong repolarization)
- Class IV: Calcium channel blockers
Chemotherapeutic Agents
Certain cancer treatments are associated with cardiotoxicity:
- 5-Fluorouracil (5-FU): Can cause arrhythmias and congestive heart failure
- Anthracyclines (e.g., doxorubicin, epirubicin): Associated with cardiomyopathy and heart failure
- Cisplatin: May lead to acute myocardial infarction
- Cyclophosphamide: Can cause acute cardiac failure and heart failure
- Taxanes (e.g., paclitaxel, docetaxel): Linked to arrhythmias and heart failure
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Toxicology – Widened QRS on ECG
Overview
The QRS complex represents ventricular depolarization and is normally less than 120 milliseconds. Because this process depends on sodium influx, any drug that blocks or delays sodium channels can prolong the QRS duration and increase the risk of dangerous arrhythmias.
Drugs That Cause QRS Widening
Tricyclic Antidepressants (TCAs)
Agents such as amitriptyline, imipramine, nortriptyline, clomipramine, and doxepin commonly cause sodium channel blockade leading to widened QRS complexes.
Class Ia Antiarrhythmics
Medications like quinidine, procainamide, and disopyramide prolong the action potential and slow conduction, resulting in QRS widening.
Class Ic Antiarrhythmics
Flecainide, propafenone, and moricizine significantly block sodium channels and can markedly widen the QRS complex.
Phenothiazines and Related Agents
Drugs such as chlorpromazine, fluphenazine, prochlorperazine, promethazine, and thioridazine, along with other agents like diphenhydramine, carbamazepine, amantadine, cocaine, and propoxyphene, may contribute to sodium channel blockade and QRS prolongation.
Other Medications
Additional drugs that may widen the QRS include venlafaxine, bupropion, citalopram, escitalopram, mesoridazine, local anesthetics (e.g., dibucaine, bupivacaine), and propranolol.
Management
Intravenous sodium bicarbonate is the primary treatment for toxin-induced QRS widening. It is especially indicated in suspected tricyclic antidepressant toxicity when the QRS duration exceeds 100 ms, regardless of blood pH. An initial dose of 1–2 mEq/kg is given as a rapid bolus and may be repeated until the QRS narrows. Continuous infusion is often required afterward, typically by adding sodium bicarbonate to intravenous fluids. Care must be taken to avoid excessive alkalemia (pH >7.55) and hypernatremia, with a target pH of approximately 7.45–7.55.
Mechanism of Antidote
Sodium bicarbonate works by increasing serum sodium concentration, helping to overcome sodium channel blockade and restore normal cardiac conduction.
Key Points
Overview
The QRS complex represents ventricular depolarization and is normally less than 120 milliseconds. Because this process depends on sodium influx, any drug that blocks or delays sodium channels can prolong the QRS duration and increase the risk of dangerous arrhythmias.
Drugs That Cause QRS Widening
Tricyclic Antidepressants (TCAs)
Agents such as amitriptyline, imipramine, nortriptyline, clomipramine, and doxepin commonly cause sodium channel blockade leading to widened QRS complexes.
Class Ia Antiarrhythmics
Medications like quinidine, procainamide, and disopyramide prolong the action potential and slow conduction, resulting in QRS widening.
Class Ic Antiarrhythmics
Flecainide, propafenone, and moricizine significantly block sodium channels and can markedly widen the QRS complex.
Phenothiazines and Related Agents
Drugs such as chlorpromazine, fluphenazine, prochlorperazine, promethazine, and thioridazine, along with other agents like diphenhydramine, carbamazepine, amantadine, cocaine, and propoxyphene, may contribute to sodium channel blockade and QRS prolongation.
Other Medications
Additional drugs that may widen the QRS include venlafaxine, bupropion, citalopram, escitalopram, mesoridazine, local anesthetics (e.g., dibucaine, bupivacaine), and propranolol.
Management
Intravenous sodium bicarbonate is the primary treatment for toxin-induced QRS widening. It is especially indicated in suspected tricyclic antidepressant toxicity when the QRS duration exceeds 100 ms, regardless of blood pH. An initial dose of 1–2 mEq/kg is given as a rapid bolus and may be repeated until the QRS narrows. Continuous infusion is often required afterward, typically by adding sodium bicarbonate to intravenous fluids. Care must be taken to avoid excessive alkalemia (pH >7.55) and hypernatremia, with a target pH of approximately 7.45–7.55.
Mechanism of Antidote
Sodium bicarbonate works by increasing serum sodium concentration, helping to overcome sodium channel blockade and restore normal cardiac conduction.
Key Points
- Sodium bicarbonate is also useful for enhancing elimination of certain toxins such as salicylates and phenobarbital.
- It is an important therapy for correcting severe metabolic acidosis in toxicologic emergencies.
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Toxicology – QT Interval Prolongation on ECG
Overview
The QT interval represents the total time for ventricular depolarization and repolarization, measured from the beginning of the Q wave to the end of the T wave. Because it varies with heart rate, the corrected QT (QTc) is used for accuracy. Normal QTc is generally less than 420 milliseconds. Prolongation occurs when potassium channel activity is impaired, delaying repolarization. When the QTc exceeds 500 milliseconds, there is a significant risk of torsades de pointes, a potentially life-threatening ventricular arrhythmia.
High-Risk Medications
Macrolide Antibiotics
Agents such as erythromycin and clarithromycin are well-known to prolong the QT interval.
Butyrophenones
Drugs like haloperidol, droperidol, and domperidone can significantly increase QT duration.
Class Ia Antiarrhythmics
Quinidine, procainamide, and disopyramide prolong cardiac repolarization and increase arrhythmia risk.
Class Ic Antiarrhythmics
Flecainide, propafenone, and moricizine can also contribute to QT prolongation.
Class III Antiarrhythmics
Medications such as amiodarone, sotalol, ibutilide, dofetilide, and dronedarone are strongly associated with QT prolongation.
Methadone
This opioid is a notable cause of QT prolongation and increases risk of torsades de pointes.
Moderate-Risk Medications
Fluoroquinolone Antibiotics
Ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin may prolong the QT interval.
Selective Serotonin Reuptake Inhibitors (SSRIs)
Fluoxetine, paroxetine, sertraline, and particularly citalopram (and less commonly escitalopram) are associated with QT prolongation.
Atypical Antipsychotics
Quetiapine, risperidone, and ziprasidone may increase QT duration.
Other Agents
Azithromycin, lithium, octreotide, and tizanidine have also been implicated in QT prolongation.
Management
Intravenous magnesium sulfate is the treatment of choice. For QTc prolongation (>500 ms), 2 g IV may be administered and repeated every 6 hours until normalization. In cases of torsades de pointes, 2 g IV should be given rapidly (over about 60 seconds) and repeated every 5–15 minutes as needed. Continuous infusion may be required for persistent arrhythmias.
Mechanism of Treatment
Magnesium stabilizes cardiac membranes and suppresses abnormal electrical activity without significantly affecting heart rate or directly shortening the QT interval.
Key Points
Overview
The QT interval represents the total time for ventricular depolarization and repolarization, measured from the beginning of the Q wave to the end of the T wave. Because it varies with heart rate, the corrected QT (QTc) is used for accuracy. Normal QTc is generally less than 420 milliseconds. Prolongation occurs when potassium channel activity is impaired, delaying repolarization. When the QTc exceeds 500 milliseconds, there is a significant risk of torsades de pointes, a potentially life-threatening ventricular arrhythmia.
High-Risk Medications
Macrolide Antibiotics
Agents such as erythromycin and clarithromycin are well-known to prolong the QT interval.
Butyrophenones
Drugs like haloperidol, droperidol, and domperidone can significantly increase QT duration.
Class Ia Antiarrhythmics
Quinidine, procainamide, and disopyramide prolong cardiac repolarization and increase arrhythmia risk.
Class Ic Antiarrhythmics
Flecainide, propafenone, and moricizine can also contribute to QT prolongation.
Class III Antiarrhythmics
Medications such as amiodarone, sotalol, ibutilide, dofetilide, and dronedarone are strongly associated with QT prolongation.
Methadone
This opioid is a notable cause of QT prolongation and increases risk of torsades de pointes.
Moderate-Risk Medications
Fluoroquinolone Antibiotics
Ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin may prolong the QT interval.
Selective Serotonin Reuptake Inhibitors (SSRIs)
Fluoxetine, paroxetine, sertraline, and particularly citalopram (and less commonly escitalopram) are associated with QT prolongation.
Atypical Antipsychotics
Quetiapine, risperidone, and ziprasidone may increase QT duration.
Other Agents
Azithromycin, lithium, octreotide, and tizanidine have also been implicated in QT prolongation.
Management
Intravenous magnesium sulfate is the treatment of choice. For QTc prolongation (>500 ms), 2 g IV may be administered and repeated every 6 hours until normalization. In cases of torsades de pointes, 2 g IV should be given rapidly (over about 60 seconds) and repeated every 5–15 minutes as needed. Continuous infusion may be required for persistent arrhythmias.
Mechanism of Treatment
Magnesium stabilizes cardiac membranes and suppresses abnormal electrical activity without significantly affecting heart rate or directly shortening the QT interval.
Key Points
- QT prolongation increases the risk of torsades de pointes, especially when QTc exceeds 500 ms.
- Among SSRIs, citalopram is most strongly associated with QT prolongation.
- Octreotide has also been recognized as a potential contributor to QT interval prolongation.
