Gastroenterology

Antidiarrheals - Loperamide & Bismuth song

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Antidiarrheals - Loperamide & Bismuth

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Key points in this song10

Loperamide is a synthetic opioid that activates μ-receptors in the myenteric plexus, decreasing peristalsis and increasing anal sphincter tone, but does NOT cross the blood-brain barrier at therapeutic doses, so it has no CNS effects or analgesic properties.
Loperamide increases water and electrolyte absorption from the gut lumen by prolonging intestinal transit time, making it effective for traveler's diarrhea and chronic diarrhea associated with IBD.
Loperamide is contraindicated in infectious diarrhea caused by invasive organisms (e.g., Shigella, Salmonella, C. difficile, EHEC O157:H7) because slowing motility promotes bacterial overgrowth and increases risk of toxic megacolon and HUS.
High-dose loperamide abuse can overcome BBB saturation, causing QTc prolongation, cardiac arrhythmias, and opioid-like CNS effects — a key FDA warning and emerging toxicology vignette.
Bismuth subsalicylate (Pepto-Bismol) has antisecretory, anti-inflammatory, and antimicrobial properties; it is a first-line agent for traveler's diarrhea prophylaxis and treatment.
Bismuth subsalicylate is a key component of quadruple therapy for H. pylori eradication (bismuth + metronidazole + tetracycline + PPI), used especially in metronidazole- or clarithromycin-resistant cases.
The salicylate component of bismuth subsalicylate is contraindicated in children with viral illnesses due to risk of Reye syndrome, and should be used cautiously in patients on aspirin or warfarin.
Bismuth causes harmless blackening of the stool and tongue due to formation of bismuth sulfide, which must be distinguished from melena.
Racecadotril (enkephalinase inhibitor) reduces intestinal hypersecretion without affecting motility, but loperamide remains the preferred OTC antidiarrheal in the United States.
Octreotide, a somatostatin analog, is the preferred agent for secretory diarrhea associated with carcinoid syndrome and VIPoma, working by inhibiting release of vasoactive peptides — distinguish this mechanism from loperamide's motility-based action.