There are some adverse effects. It can cause a black tongue and black stools in some users of the drug when it combines with trace amounts of sulfur in saliva and the colon to form bismuth sulfide. Bismuth sulfide is a highly insoluble black salt, and the discoloration seen is temporary and harmless.
Long-term use (greater than 6 weeks) may lead to accumulation and toxicity. Some of the risks of salicylism can apply to the use of bismuth subsalicylate.
Children should not take medication with bismuth subsalicylate while recovering from influenza or chicken pox, as epidemiologic evidence points to an association between the use of salicylate-containing medications during certain viral infections and the onset of Reye syndrome. For the same reason, it is typically recommended that nursing mothers not use medication containing bismuth subsalicylate because small amounts of the medication are excreted in human breast milk, and these pose a theoretical risk of Reye's syndrome to nursing children.
Salicylates are very toxic to cats, and thus bismuth subsalicylate should not be administered to cats.
The British National Formulary does not recommend bismuth-containing antacids (unless chelated), cautioning that absorbed bismuth can be neurotoxic, causing encephalopathy, and that such antacids tend to be constipating.
Mechanism of action
Bismuth subsalicylate is used as an antacid and antidiarrheal, and to treat some other gastrointestinal symptoms, such as nausea. The means by which this occurs is still not well documented. It is thought to be some combination of the following:
Stimulation of absorption of fluids and electrolytes by the intestinal wall (antisecretory action)
As a salicylate, reducing inflammation/irritation of stomach and intestinal lining through inhibition of prostaglandin G/H synthase 1/2
Reduction in hypermotility of the stomach
Binding of toxins produced by Escherichia coli
Bactericidal action of a number of its subcomponents, including salicylic acid
Bactericidal action via a so-called oligodynamic effect in which small amounts of heavy metals such as bismuth damage many different bacteria species.
Weak antacid properties
In vitro and in vivo data have shown that bismuth subsalicylate hydrolyzes in the gut to bismuth oxychloride and salicylic acid and less commonly bismuth hydroxide. In the stomach, this is likely an acid-catalyzed hydrolysis. The salicylic acid is absorbed and therapeutical concentrations of salicylic acid can be found in blood after bismuth subsalicylate administration. Bismuth oxychloride and bismuth hydroxide are both believed to have bactericidal effects, as is salicylic acid for enterotoxigenic E. coli a common cause of "traveler's diarrhea."
Organobismuth compounds have historically been used in growth media for selective isolation of microorganisms. Such salts have been shown to inhibit proliferation of Helicobacter pylori, other enteric bacteria, and some fungi.
Bismuth slag from decomposition of Pepto-Bismol
Bismuth subsalicylate is the only active ingredient in an over-the-counter drug that can leave a shiny metal oxideslag behind after being completely burnt with a blow torch.
1957 Life magazine ad for the product
While bismuth salts were in use in Europe by the late 1700s, the combination of bismuth subsalicylate and zinc salts for astringency with salol (phenyl salicilate) appears to have begun in the US in the early 1900s as a remedy for life-threatening diarrhea in infants with cholera. At first sold directly to physicians, it was first marketed as Bismosal in 1918.
Pepto-Bismol began being sold in 1900 or 1901 by a doctor in New York. It was originally sold as a remedy for infant diarrhea by Norwich Pharmacal Company under the name "Bismosal: Mixture Cholera Infantum". It was renamed Pepto-Bismol in 1919. Norwich Eaton Pharmaceuticals was acquired by Procter and Gamble in 1982.
As of 1946 and 1959, Canadian advertisements placed by Norwich show the product as Pepto-Besmal both in graphic and text.
Pepto-Bismol is an over-the-counter drug currently produced by the Procter & Gamble company in the United States, Canada and the United Kingdom. Pepto-Bismol is made in chewable tablets and swallowable caplets, but it is best known for its original formula, which is a thick liquid. This original formula is a medium pink in color, with a teaberry (methyl salicylate) flavor.
^Madisch A, Morgner A, Stolte M, Miehlke S (December 2008). "Investigational treatment options in microscopic colitis". Expert Opinion on Investigational Drugs. 17 (12): 1829-37. doi:10.1517/13543780802514500. PMID19012499.
^Vernace MA, Bellucci AG, Wilkes BM (September 1994). "Chronic salicylate toxicity due to consumption of over-the-counter bismuth subsalicylate". The American Journal of Medicine. 97 (3): 308-9. doi:10.1016/0002-9343(94)90017-5. PMID8092182.
Andrews PC, Deacon GB, Forsyth CM, Junk PC, Kumar I, Maguire M (August 2006). "Towards a structural understanding of the anti-ulcer and anti-gastritis drug bismuth subsalicylate". Angewandte Chemie. 45 (34): 5638-42. doi:10.1002/anie.200600469. PMID16865763.