Bismuth Subsalicylate - Mechanism of Action

Mechanism of Action

Bismuth subsalicylate is used as an antacid and antidiarrheal, and to treat some other gastro-intestinal diseases, such as nausea. It is the active ingredient in various stomach-settling medications, including Pepto-Bismol.
The means by which this occurs is still not well documented. It is thought to be some combination of the following:

• Retarding the expulsion of fluids into the digestive system by irritated tissues, by "coating" them.
• Stimulation of absorption of fluids and electrolytes by the intestinal wall (antisecretory action)
• 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 E. 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 are toxic for a number of microbes.
• Weak antacid properties

In vitro and in vivo data has 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 adsorbed and therapeutical concentration 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 Escherichia 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 H. pylori, other enteric bacteria, and some fungi.