Prescribing-label excerpts
Loperamide Hydrochloride
Reference for: Loperamide Hcl. Source presentation: capsule. Source route: oral.
The source label presents its clinical-pharmacology findings together. These selected passages retain the source’s study context; the full label provides the complete discussion.
Clinical pharmacology
Mechanism of Action — In vitro and animal studies show that loperamide hydrochloride acts by slowing intestinal motility and by affecting water and electrolyte movement through the bowel. Loperamide binds to the opiate receptor in the gut wall. Consequently, it inhibits the release of acetylcholine and prostaglandins, thereby reducing propulsive peristalsis, and increasing intestinal transit time. Loperamide increases the tone of the anal sphincter, thereby reducing incontinence and urgency.
Pharmacodynamics — Loperamide prolongs the transit time of the intestinal contents. It reduces 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.
Absorption — Plasma concentrations of unchanged drug remain below 2 ng/mL after the intake of a 2 mg capsule of loperamide hydrochloride. Plasma loperamide concentrations are highest approximately 5 hours after administration of the capsule and 2.5 hours after the liquid. The peak plasma concentrations of loperamide were similar for both formulations.
Distribution — Based on literature information, the plasma protein binding of loperamide is about 95%. Loperamide is a P-glycoprotein substrate.
Elimination — The apparent elimination half-life of loperamide is 10.8 hours with a range of 9.1 to 14.4 hours. Elimination of loperamide mainly occurs by oxidative N-demethylation.
Metabolism — In vitro loperamide is metabolized mainly by cytochrome P450 (CYP450) isozymes, CYP2C8 and CYP3A4, to form- N-demethyl loperamide. In an in vitro study quercetin (CYP2C8 inhibitor) and ketoconazole (CYP3A4 inhibitor) significantly inhibited the N-demethylation process by 40% and 90%, respectively. In addition, CYP2B6 and CYP2D6 appear to play a minor role in loperamide N-demethylation.
Concomitant use of loperamide hydrochloride with inhibitors of CYP3A4 (e.g., itraconazole) or CYP2C8 (e.g., gemfibrozil) or inhibitors of P-glycoprotein (e.g., quinidine, ritonavir) can increase exposure to loperamide (see PRECAUTIONS, Drug Interactions).
Excretion — Excretion of the unchanged loperamide and its metabolites mainly occurs through the feces.
Selected passages from the cited U.S. prescribing label. The studies concern the source product and populations named in each passage; they do not establish Walter-product bioequivalence, an approved indication, or the kinetics of another fixed combination. Tables and the full prescribing information remain available in the source.
Source: DailyMed: Loperamide Hydrochloride — capsule
Reference accessed . Label revision: 2026-08-25.