Toxicology – Bismuth

Core concept

Bismuth toxicity is uncommon and usually occurs after excessive or prolonged exposure rather than a single therapeutic dose.

The most important toxic syndromes are:

Acute/high-dose bismuth exposure → nephrotoxicity

Chronic excessive exposure → encephalopathy

With bismuth subsalicylate, always remember a second toxic component:

Salicylate toxicity may occur independently of bismuth toxicity.

Renal impairment increases the risk of bismuth accumulation and adverse effects.

Forms

Bismuth compounds include:

• Bismuth subsalicylate
• Bismuth subcitrate
• Bismuth subcarbonate
• Bismuth subgallate
• Bismuth subnitrate
• Other inorganic and organic bismuth salts

The most familiar OTC preparation is bismuth subsalicylate.

Current Pepto-Bismol formulations contain 262 mg bismuth subsalicylate per caplet or 525 mg per 30 mL dose, depending on formulation.

Uses

Bismuth-containing products are used for:

• Diarrhea
• Traveler’s diarrhea
• Dyspepsia
• Nausea
• Indigestion
• Combination therapy for Helicobacter pylori

Toxic Dose

There is no single well-established toxic dose applicable to all bismuth compounds.

Toxicity depends on:

• Chemical form
• Solubility
• Duration of exposure
• Renal function
• Dose
• Route of administration

Single therapeutic ingestions rarely cause major bismuth toxicity.

Significant poisoning is more often associated with:

• Chronic excessive use
• Large intentional ingestion
• Renal impairment
• Historically, parenteral bismuth preparations

Pathophysiology

Bismuth absorption varies greatly according to the compound.

Many medicinal bismuth salts are poorly absorbed from the gastrointestinal tract, but the absorbed fraction may:

• Accumulate in tissues
• Concentrate in the kidney
• Persist for prolonged periods

Bismuth has been detected in:

• Kidneys
• Nervous tissue
• Bone
• Liver

The kidney is particularly important because absorbed bismuth is largely handled through renal elimination. Patients with impaired renal function may therefore accumulate higher concentrations.

Bismuth Subsalicylate

Bismuth subsalicylate produces two clinically distinct potential problems:

1. Bismuth toxicity

May cause:

• Encephalopathy
• Nephrotoxicity

2. Salicylate toxicity

May cause:

• Tinnitus
• Tachypnea
• Vomiting
• Acid-base abnormalities
• Altered mental status
• Pulmonary edema
• Severe metabolic toxicity

Bismuth subsalicylate is a recognized source of salicylate poisoning, particularly with chronic excessive use.

Clinical Features

Gastrointestinal

Possible effects include:

• Nausea
• Vomiting
• Diarrhea
• Abdominal discomfort

Black tongue and stool

Bismuth commonly causes a temporary darkening of the tongue and stool.

This is generally harmless and is specifically described in current product labeling.

This benign effect must be distinguished from:

• Melena
• Gastrointestinal bleeding

HEENT

Chronic toxicity has historically been associated with:

• Increased salivation
• Gingivitis
• Stomatitis
• Bluish gingival discoloration

These findings are now uncommon.

Tinnitus

With bismuth subsalicylate, ringing in the ears or hearing changes may indicate clinically significant salicylate exposure.

Current OTC labeling advises stopping the drug and seeking medical advice if tinnitus or hearing loss occurs.

Neurologic

Chronic excessive bismuth exposure can produce bismuth encephalopathy.

Early manifestations may include:

• Malaise
• Headache
• Irritability
• Reduced concentration
• Memory disturbance
• Confusion

Progressive toxicity may produce:

• Dysarthria
• Ataxia
• Gait disturbance
• Tremor
• Myoclonus
• Hallucinations
• Somnolence
• Seizures
• Severe encephalopathy

Chronic bismuth exposure has repeatedly been associated with neurologic toxicity, especially when renal function is impaired.

Renal

The kidney is a major target of significant bismuth toxicity.

Possible abnormalities include:

• Proteinuria
• Hematuria
• Acute tubular injury
• Fanconi-type proximal tubular dysfunction
• Oliguria
• Anuria
• Acute kidney injury

A systematic review of reported human toxicity found kidney injury predominantly after medically related excessive exposures and noted worse outcomes in patients with pre-existing renal dysfunction.

Hepatic

Rare reported effects include:

• Elevated transaminases
• Hepatic dysfunction

Severe liver toxicity is much less characteristic than neurologic or renal injury.

Musculoskeletal

Historical chronic exposure has been associated with:

• Bone deposition
• Osteoarthropathy
• Osteomalacia

These manifestations are uncommon with contemporary therapeutic use.

Hematologic

Some unusual bismuth compounds may indirectly contribute to oxidative or nitrate-related toxicity.

However, with bismuth subsalicylate, the more clinically important hematologic/toxicologic concern is usually the salicylate component rather than direct hematologic toxicity from bismuth.

Diagnosis

Clinical Diagnosis

Think of bismuth toxicity when there is:

Prolonged bismuth use + altered mental status or neurologic abnormalities ± renal dysfunction

For bismuth subsalicylate, also consider:

Chronic OTC use + tinnitus/tachypnea/confusion → salicylate toxicity

Essential Investigations

For symptomatic or significantly exposed patients consider:

• Serum electrolytes
• Bicarbonate
• BUN
• Creatinine
• Glucose
• Urinalysis
• Liver enzymes
• CBC

Salicylate Level

A serum salicylate concentration is essential when bismuth subsalicylate toxicity is suspected.

Remember that chronic salicylate toxicity can be severe at concentrations lower than those seen in acute overdose, so the number must be interpreted together with:

• Symptoms
• Acid-base status
• Renal function
• Timing of exposure

Blood Gas

Obtain a blood gas when significant salicylate toxicity is suspected.

Typical salicylate poisoning may produce:

• Respiratory alkalosis
• Metabolic acidosis
• Mixed acid-base disturbances

Bismuth Concentration

Blood or urine bismuth concentrations can help confirm excessive exposure.

However:

Bismuth levels correlate imperfectly with clinical severity and should not replace clinical assessment.

Testing often requires a specialized reference laboratory.

Differential Diagnosis

For encephalopathy consider:

• Salicylate poisoning
• Lead poisoning
• Mercury poisoning
• Medication toxicity
• Uremia
• Hepatic encephalopathy
• CNS infection
• Structural neurologic disease

For renal injury consider:

• Other heavy metals
• Nephrotoxic medications
• Ischemic acute tubular injury
• Glomerular disease
• Other causes of Fanconi syndrome

Treatment

1. Stop Bismuth Exposure

Immediately discontinue the bismuth-containing product.

This is the most important intervention in chronic toxicity.

Also identify:

• Duration of exposure
• Daily dose
• Exact formulation
• Other salicylate-containing products
• Renal disease
• Coingestants

2. Supportive Care

Provide:

• Airway support when necessary
• IV fluids when appropriate
• Electrolyte correction
• Seizure treatment
• Renal support

Management should be guided by the dominant syndrome:

• Bismuth neurotoxicity
• Renal failure
• Salicylate poisoning

Gastrointestinal Decontamination

Do Not Induce Vomiting

The historical recommendation to use ipecac-induced emesis is obsolete.

Do not induce vomiting.

Activated Charcoal

Activated charcoal may be considered after a significant recent acute ingestion, particularly when salicylate-containing bismuth preparations are involved, provided:

• The airway is protected
• Aspiration risk is acceptable

Activated charcoal has a more established role for the salicylate component than for systemic bismuth already absorbed.

Gastric Lavage

Routine gastric lavage is not recommended in contemporary poisoning management.

It would only be considered in exceptional circumstances after specialist toxicology consultation.

Salicylate Toxicity from Bismuth Subsalicylate

When salicylate poisoning is clinically significant, treatment follows standard salicylate-poisoning principles.

Volume and Electrolyte Correction

Correct:

• Dehydration
• Potassium abnormalities
• Glucose abnormalities

Adequate intravascular volume and renal perfusion are important for salicylate elimination.

Sodium Bicarbonate

For clinically important salicylate poisoning:

IV sodium bicarbonate is used to alkalinize serum and urine and enhance salicylate elimination.

Urinary alkalinization significantly increases renal salicylate clearance.

Hemodialysis

Hemodialysis may be required for severe salicylate poisoning, particularly with:

• Severe neurologic toxicity
• Pulmonary edema
• Significant acidemia
• Renal failure
• Deterioration despite appropriate therapy

Hemodialysis for Bismuth

Hemodialysis has also been used in severe bismuth poisoning associated with acute kidney injury.

However, bismuth may redistribute from tissue stores back into blood after dialysis, so reduction in circulating concentrations may be transient.

Dialysis is therefore most clearly indicated when there are conventional indications such as:

• Severe renal failure
• Electrolyte disturbances
• Acid-base abnormalities
• Severe associated salicylate toxicity

Chelation Therapy

Older references recommend:

• Dimercaprol (BAL)
• D-penicillamine

These are not established routine antidotes for contemporary bismuth poisoning.

Various chelators, including sulfur-containing compounds such as DMPS, have been described in individual cases, but the evidence base consists largely of case reports rather than controlled clinical data.

Therefore:

Chelation should only be considered in severe confirmed bismuth poisoning with medical-toxicology consultation.

Antidote

There is no universally accepted specific antidote for bismuth toxicity.

Treatment is primarily:

• Cessation of exposure
• Supportive care
• Management of renal failure
• Treatment of accompanying salicylate toxicity

Monitoring

For clinically significant toxicity monitor:

• Mental status
• Renal function
• Electrolytes
• Acid-base status
• Urine output

With bismuth subsalicylate exposure also monitor:

• Serial salicylate concentrations
• Respiratory status
• Glucose
• Potassium

Admission

Hospital admission is appropriate for:

• Altered mental status
• Encephalopathy
• Significant renal dysfunction
• Severe salicylate toxicity
• Acid-base disturbance
• Seizures
• Persistent vomiting
• Other clinically significant systemic effects

Severe neurologic or metabolic toxicity may require ICU management.

Pediatric Considerations

Because bismuth subsalicylate contains salicylate, special caution is required in children and adolescents.

Current product labeling states that:

Children and teenagers who have or are recovering from chickenpox or influenza-like illness should not use bismuth subsalicylate because of the risk of Reye syndrome.

Thus, the older blanket statement that it must always be avoided in everyone under age 16 is less precise than current U.S. labeling.

Drug Interactions and Precautions

Current labeling advises against concurrent use in patients:

• Allergic to aspirin or salicylates
• Taking other salicylate products

Medical or pharmacist review is advised when patients are taking drugs for:

• Anticoagulation
• Diabetes
• Gout
• Arthritis

Prognosis

Most therapeutic exposures do not cause serious toxicity.

With significant poisoning:

• Acute kidney injury may take days to weeks to recover
• Severe renal failure may require prolonged dialysis
• Neurologic abnormalities may resolve slowly
• Chronic encephalopathy can require weeks or longer for recovery

Case literature documents recovery after severe bismuth-associated neurologic and renal toxicity, although persistent renal injury has also occurred.

Important Pitfalls

1. Forgetting the salicylate component

With bismuth subsalicylate, toxicity may actually be predominantly salicylate poisoning.

Always consider a salicylate level in a symptomatic patient.

2. Missing chronic OTC use

Patients may not consider products such as Pepto-Bismol to be “medications.”

Ask specifically about:

• OTC diarrhea remedies
• Dyspepsia preparations
• Duration and frequency of use

3. Misinterpreting black stool

Bismuth commonly causes harmless blackening of the stool and tongue.

However, true GI bleeding must still be excluded when clinically appropriate.

4. Missing renal impairment

Reduced renal function increases the risk of accumulation and severe bismuth toxicity.

5. Using ipecac

Ipecac-induced vomiting is obsolete and should not be used.

6. Assuming chelation is routinely indicated

Evidence supporting chelation in bismuth poisoning is limited.

Treatment is primarily withdrawal of exposure and supportive care.

High-Yield Toxicology Pearls

Bismuth toxicity = chronic encephalopathy + renal injury

With bismuth subsalicylate, also think:

SALICYLATE TOXICITY

Key points:

• Poisoning is uncommon
• Significant toxicity usually follows large or prolonged exposure
• Chronic toxicity may cause encephalopathy
• Acute large exposures may produce acute kidney injury
• Renal impairment increases toxicity risk
• Bismuth levels may confirm exposure but correlate poorly with severity
• Bismuth subsalicylate can cause clinically important salicylate poisoning
• Check a serum salicylate level in symptomatic bismuth-subsalicylate exposure
• Tinnitus is an important clue to salicylate toxicity
• Black tongue and stool are common and usually benign
• Severe salicylate toxicity requires sodium bicarbonate ± hemodialysis
• No universally accepted bismuth antidote exists
• Chelation is not routine
• Do not induce vomiting
• Children and teenagers with influenza-like illness or chickenpox should not receive bismuth subsalicylate because of the risk of Reye syndrome