The inactive ingredients are: corn starch, lactose monohydrate, magnesium stearate and talc. The capsule shell contains gelatin, iron oxide red, iron oxide yellow and sodium lauryl sulfate. The capsules are imprinted with black ink containing black iron oxide, potassium hydroxide, propylene glycol and shellac.

FDA approved dissolution test specifications differ from USP.

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.

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.