Bismuth Subsalicylate
Properties
| State | Solid (insoluble powder) |
| Color | Pink to white |
| Solubility | Insoluble in water, ethanol, and most organic solvents; slowly dissolves in dilute HCl |
About Bismuth Subsalicylate
Bismuth subsalicylate is the active ingredient in Pepto-Bismol, and chemically it is one of the more frustrating compounds in the OTC cabinet — the formula C7H5BiO4 (molar mass 362.093 g/mol) describes only the simplest repeat unit of what is actually a coordination polymer of Bi(III) bridged by salicylate carboxylates and oxide ligands, with chain length and stoichiometry varying by synthesis route. The material is so insoluble in everything (water, ethanol, DMSO, most organic solvents) that crystallographers have struggled to pin down a definitive structure for decades, and most published 'structures' are actually X-ray pair-distribution function fits rather than single-crystal solutions. Despite that ambiguity, the pharmacology is well-characterized: salicylate provides mild antisecretory and anti-inflammatory action on the gut mucosa via COX inhibition, while Bi(III) does the heavy lifting by binding sulfhydryl groups in bacterial enterotoxins (notably the heat-labile toxin from ETEC), coating the gut lining with a protective bismuth-protein layer, and showing direct bactericidal activity against Helicobacter pylori. That last property is why BSS is one of four drugs in 'bismuth quadruple therapy' (BSS plus a PPI plus metronidazole plus tetracycline) — a regimen the Maastricht VI/Florence consensus and ACG recommend for clarithromycin-resistant H. pylori, which now accounts for over 30 percent of strains in much of the world.
Where you'll encounter it
If you've ever taken Pepto-Bismol on a trip to Mexico or after a questionable taco, you've encountered BSS. In a hospital setting, gastroenterologists prescribe it as part of quadruple therapy for H. pylori — patients take 524 mg four times daily for 14 days alongside the antibiotics and PPI. The drug is also a fixture of expedition medicine: Studies in volunteers traveling to high-risk regions show two tablets four times daily reduces traveler's diarrhea incidence by about 65 percent, which is why CDC's Yellow Book lists it as an evidence-based prophylactic option.
Common Uses
- Active ingredient in OTC antidiarrheals (Pepto-Bismol, Kaopectate) at 262 mg per dose
- Bismuth quadruple therapy component for clarithromycin-resistant H. pylori eradication
- Traveler's diarrhea prophylaxis at two tablets four times daily, per CDC Yellow Book
- Symptomatic relief of dyspepsia, nausea, and mild gastric irritation
- Adjunct in peptic ulcer regimens for patients intolerant of standard triple therapy
Safety Information
GHS: Acute toxicity oral Category 5. The salicylate moiety is the practical concern — pediatric use carries Reye syndrome risk identical to aspirin, and patients on warfarin need INR monitoring because salicylate displaces it from albumin. Long-term high-dose use (over 8 weeks at maximum dose) has been linked to reversible bismuth encephalopathy with myoclonus, ataxia, and cognitive changes; case series from the 1970s in France documented this in habitual users. Avoid in pregnancy (third trimester especially) and concurrent tetracyclines, since Bi(III) chelates them and tanks oral bioavailability.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.