Loperamide, a synthetic piperidine derivative, is a drug effective against diarrhea resulting from gastroenteritis or inflammatory bowel disease. In most countries it is available generically and under brand names such as Lopex, Imodium, Dimor and Pepto Diarrhea Control. It was discovered at Janssen Pharmaceutica in 1969.
It works by decreasing the activity of the myenteric plexus which decreases the motility of the circular and longitudinal smooth muscles of the intestinal wall. This increases the amount of time substances stay in the intestine, allowing for more water to be absorbed out of the fecal matter. Loperamide also decreases colonic mass movements and suppresses the gastrocolic reflex.
Loperamide molecules do not cross the blood-brain barrier in significant amounts, and thus it has no analgesic properties. Any that do cross the blood-brain barrier are quickly exported from the brain by P-glycoprotein (Pgp), also known as multidrug resistance protein (MDR1). Tolerance in response to long-term use has not been reported.
However, loperamide can cause physical dependence. Symptoms of opiate withdrawal have been observed in patients abruptly discontinuing long-term therapy with loperamide. For this reason, the drug was briefly classified as a Schedule V controlled substance upon its introduction.fever or if the stool is bloody. Treatment is not recommended for patients who could suffer detrimental effects from rebound constipation. If there is a suspicion of diarrhea associated with organisms that can penetrate the intestinal walls, such as H7 or salmonella, loperamide is contraindicated.
Concurrent administration of P-glycoprotein inhibitors such as quinidine with loperamide has been found to produce respiratory depression, indicative of central opioid action.