The mechanism of action of diphenoxylate (Lotomil) is:
A. An increase in intestinal excretion of water.
B. An increase in intestinal motility.
C. A decrease in peristalsis in the intestinal wall.
D. A decrease in the reabsorption of water in the bowel.
Correct Answer: C. A decrease in peristalsis in the intestinal wall.
Diphenoxylate acts on the smooth muscle of the intestinal tract to inhibit GI motility and excessive propulsion of the GI tract (peristalsis). Diphenoxylate is an active ingredient of commonly available antimotility agents. Its indication is for the treatment of diarrhea in adults and children 13 years or older, or as add-on therapy in the management of acute non-infectious diarrhea.
Option A: By acting on the presynaptic opioid receptors, it blocks the release of acetylcholine in the synaptic cleft and hence inhibits the motility and secretory action of the enteric nervous system. This action leads to a decrease in segmental contractions and prolongation of gastrointestinal transit time. Diphenoxylate reduces the epithelial secretion of fluid and electrolytes and enhances active absorption by mild action on delta receptors.
Option B: It does not have analgesic effects of morphine at standard doses, but at higher doses, it can lead to CNS effects, like euphoria. The drug can have a misuse potential if used for a prolonged time and classified as Schedule V drug under Food and Drug Administration.
Option D: Diphenoxylate can precipitate GI complications, including sepsis and prolonged diarrhea, when administered in patients with infectious diarrhea. This effect is because of the prolongation of GI transit time and decreased GI motility, which leads to bacterial overgrowth and release of enterotoxins into the bloodstream, creating a septic shock-like picture.
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