Does elevated urinary bismuth indicate exposure but not prove neurotoxicity?

Bismuth is usually absorbed only to a limited extent from oral products, but absorbed drug distributes to tissues—particularly kidney—and is eliminated partly in urine. In a 77-year-old, kidney function and cumulative exposure are especially important when interpreting results.

Interpretation of urinary bismuth

• An elevated urine bismuth result credibly indicates recent or prior bismuth exposure and active renal elimination. Human tracer studies show initially rapid, predominantly urinary elimination after intravenous bismuth-207.
• It is not a validated quantitative estimate of total-body, renal, or brain bismuth burden. Urine values vary with formulation, dose, duration, timing of last use, urine dilution, random versus 24-hour collection, and renal function. Urinary elevation may persist after blood concentrations have fallen.
• A urine result alone cannot diagnose bismuth neurotoxicity. If encephalopathy is suspected, assessment requires a compatible neurologic syndrome, detailed exposure history, renal evaluation, exclusion of alternative causes, and preferably whole-blood bismuth; EEG diffuse slowing may be supportive.

Neurotoxicity and mechanisms

• Sustained substantial exposure can cause bismuth encephalopathy. In a French series of 45 patients taking bismuth subnitrate 5–20 g/day for 4 weeks to 30 years, blood bismuth was 150–1,600 µg/L and urine bismuth 200–9,600 µg/L.
• Typical manifestations include confusion or behavioral change, myoclonus, tremor, dysarthria, impaired coordination/gait, and occasionally seizures. Improvement after stopping bismuth supports causality.
• Renal impairment can increase systemic accumulation: a small study found 3- to 5-fold trough plasma accumulation correlated with creatinine clearance. Encephalopathy has occurred at 864 mg/day for two months in a person with pre-existing renal impairment.

Bottom line

• Elevated urinary bismuth establishes exposure and renal excretion, but neither quantifies tissue burden nor proves neurotoxicity. Prolonged or high exposure can cause encephalopathy, particularly with impaired kidney function; neurologic symptoms warrant prompt discontinuation of all bismuth products and urgent clinical/toxicology assessment.