Loperamide is a synthetic piperidine derivative, a long-acting antidiarrheal agent that acts primarily via opioid μ-receptors in the myenteric plexus of the large intestine. It is a first-line symptomatic treatment for acute, chronic, and traveler's diarrhea in the Indian context, widely available as an over-the-counter (OTC) medicine. It is not an antibiotic and does not treat the underlying infectious cause of diarrhea.
Adult: Acute Diarrhea: Initial dose 4 mg (two 2mg tablets), followed by 2 mg after each unformed stool. Maximum: 16 mg per day. Chronic Diarrhea: Individualized maintenance dose, typically 4-8 mg/day in divided doses.
Note: Take orally with or without food. Swallow tablet whole with a glass of water. Do not crush or chew. For acute diarrhea, if no improvement after 48 hours, discontinue and consult a physician.
Loperamide is a peripherally-acting μ-opioid receptor agonist. It acts locally on the opioid receptors in the myenteric plexus of the intestinal wall. This action inhibits the release of acetylcholine and prostaglandins, thereby decreasing peristalsis and increasing intestinal transit time. It also enhances anal sphincter tone and reduces daily fecal volume, increases viscosity, and diminishes fluid and electrolyte loss.
Pregnancy: Category C (US FDA). Animal studies have shown adverse effects. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Avoid in first trimester unless absolutely necessary.
Driving: May cause dizziness or drowsiness. Patients should not drive or operate machinery until they know how the drug affects them.
| CYP3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Ritonavir, Clarithromycin, Grapefruit juice) | Markedly increases loperamide plasma levels, increasing risk of QT prolongation and CNS toxicity. | Major |
| CYP2C8 Inhibitors (e.g., Gemfibrozil) | Increases loperamide levels. | Moderate |
| CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine, Phenytoin, St. John's Wort) | May decrease loperamide efficacy. | Moderate |
| Other CNS Depressants (e.g., Alcohol, Benzodiazepines, Opioids) | Additive CNS depression (drowsiness, dizziness). | Moderate |
| Anticholinergic Drugs (e.g., Atropine, Tricyclic Antidepressants) | Increased risk of paralytic ileus and severe constipation. | Moderate |
| QT-prolonging Drugs (e.g., Amiodarone, Sotalol, certain Antipsychotics, Macrolides) | Additive risk of cardiac arrhythmias, especially with loperamide overdose. | Major |