| Indication | For the control and symptomatic relief of acute nonspecific diarrhea and of chronic diarrhea associated with inflammatory bowel disease or gastroenteritis. Also used for reducing the volume of discharge from ileostomies. |
| Pharmacodynamics | Loperamide is a synthetic anti-diarrheal indicated for the control and symptomatic relief of acute nonspecific diarrhea and of chronic diarrhea associated with inflammatory bowel disease. Loperamide is also indicated for reducing the volume of discharge from ileostomies. In man, Loperamide prolongs the transit time of the intestinal contents. It reduces the daily fecal volume, increases the viscosity and bulk density, and diminishes the loss of fluid and electrolytes. Tolerance to the antidiarrheal effect has not been observed. Loperamide is an opioid receptor agonist and acts on the mu opioid receptors in the myenteric plexus large intestines; it does not affect the central nervous system like other opioids. It works specifically 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. |
| Mechanism of action | In vitro and animal studies show that Loperamide acts by slowing intestinal motility and by affecting water and electrolyte movement through the bowel. Loperamide inhibits peristaltic activity by a direct effect on the circular and longitudinal muscles of the intestinal wall. It is a non-selective calcium channel blocker and binds to opioid mu-receptors. Evidence also suggests that at higher concentrations it binds to calmodulin. |
| Absorption | Not significantly absorbed from the gut |
| Volume of distribution | Not Available |
| Protein binding | 97% |
| Metabolism | Hepatic |
| Route of elimination | Excretion of the unchanged loperamide and its metabolites mainly occurs through the feces. |
| Half life | 9.1 to 14.4 hours (average 10.8 hours) |
| Clearance | Not Available |
| Toxicity | Oral, mouse: LD50 = 105 mg/kg. Symptoms of overdose include constipation, drowsiness, lethargy, and nausea. |