bismuth

**Formulations:** Bismuth subsalicylate (BSS; Pepto-Bismol, Kaopectate in some formulations) and bismuth subcitrate (in Pylera and other H. pylori regimens).

**Mechanism of action:** - Coats ulcer craters and the GI mucosa, forming a protective barrier. - Direct bactericidal effect on H. pylori (disrupts cell wall and inhibits urease, ATP synthesis, and adherence). - Antisecretory and anti-inflammatory effect. The salicylate moiety inhibits prostaglandin synthesis, which reduces intestinal secretion and inflammation. This is why BSS helps in secretory (traveler's/ETEC) diarrhea. - Binds bacterial enterotoxins (e.g., ETEC, V. cholerae toxin). - Stimulates mucosal prostaglandin and bicarbonate secretion, promoting ulcer healing.

**Clinical uses:** - H. pylori eradication. Bismuth quadruple therapy = bismuth + PPI + tetracycline + metronidazole for 10–14 days. It is a preferred first-line option in many guidelines, especially with clarithromycin resistance or penicillin allergy. - Traveler's diarrhea (prevention and treatment). - Nonulcer dyspepsia, nausea, and heartburn. - Peptic ulcer disease (adjunct).

**Adverse effects and toxicity:** - Black tongue and black stools. These are benign and due to bismuth sulfide formation. They can mimic melena, so distinguish by guaiac testing (bismuth is guaiac-negative). - Salicylate toxicity: tinnitus, especially with high doses or in renal impairment. Avoid in aspirin/salicylate allergy and with anticoagulants (additive bleeding risk). - Reye syndrome risk in children with viral illness (influenza, varicella). Avoid in children and teenagers recovering from these infections. - Bismuth encephalopathy with chronic, high-dose use: confusion, myoclonus, ataxia, and tremor. It is typically reversible after discontinuation. Nephrotoxicity is also possible. - Can reduce absorption of tetracyclines and fluoroquinolones. - Relatively contraindicated in renal failure.

**Boards pearls:** - The black stool/tongue question is a classic. Bismuth is the cause, and the stool is guaiac-negative. - Bismuth is part of the H. pylori quadruple regimen (PBMT: PPI, Bismuth, Metronidazole, Tetracycline). - Mechanisms to recall: coating, antimicrobial action, and antisecretory action (via salicylate/prostaglandin inhibition). - Similar GI mucosal protectant: sucralfate, which binds ulcer bases in an acidic environment and needs an acidic pH to be activated. It is not an acid suppressor. - Avoid in kids with viral illnesses (Reye syndrome) and in patients on warfarin or with salicylate allergy.