IMODIUM
Clinical safety rating: caution
Comprehensive clinical and safety monograph for IMODIUM (IMODIUM).
Loperamide is a peripheral mu-opioid receptor agonist that inhibits peristalsis and prolongs transit time by reducing smooth muscle motility in the gastrointestinal tract. It also increases anal sphincter tone and decreases secretion, leading to reduced stool frequency and increased consistency.
| Metabolism | Primarily hepatic via CYP2C8 and CYP3A4; undergoes glucuronidation; loperamide is a substrate for P-glycoprotein (P-gp). |
| Excretion | Primarily fecal (90-95% as unchanged drug and glucuronide conjugates), renal (<2% unchanged, ~10% as metabolites). Biliary excretion is the major route for conjugated metabolites. |
| Half-life | Terminal elimination half-life is approximately 9-14 hours (mean 10.8 h). In patients with hepatic impairment, half-life may be prolonged, requiring dose adjustment. |
| Protein binding | ~95-97% bound, primarily to albumin. |
| Volume of Distribution | Vd ~2.5-3.7 L/kg. Large Vd indicates extensive tissue distribution, but clinically minimal CNS penetration due to P-glycoprotein efflux at the blood-brain barrier. |
| Bioavailability | Oral bioavailability is ~40% (range 30-60%) due to extensive first-pass metabolism (glucuronidation in liver and intestinal wall). |
| Onset of Action | Oral (capsule/tablet): 0.5-1 hour. Oral (liquid): 0.5-1 hour. Onset may be faster with liquid formulation due to more rapid absorption. |
| Duration of Action | 4-6 hours for antidiarrheal effect. Clinical duration may be longer (up to 12 hours) due to sustained opioid receptor binding in the gut. |
| Molecular Weight | 477.04 |
| Action Class | Opioid Agonist- Antidiarrheal |
| Brand Substitutes | Loopra 2mg Capsule, Loprapil 2mg Capsule, Lomax 2mg Capsule, Nelop 2mg Capsule, HG Mide 2mg Capsule |
4 mg orally initially, followed by 2 mg after each unformed stool, not exceeding 16 mg/day. For chronic diarrhea: 4-8 mg/day in divided doses. Max 16 mg/day.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment. Use caution in severe renal impairment (CrCl <30 mL/min) due to potential for CNS effects. |
| Liver impairment | In Child-Pugh A: no adjustment. Child-Pugh B: reduce initial dose to 2 mg, titrate cautiously. Child-Pugh C: contraindicated. |
| Pediatric use | Children 6-11 years (20-35 kg): 2 mg orally after first unformed stool, then 1 mg after each subsequent stool, max 6 mg/day. Children 12-17 years: adult dosing. |
| Geriatric use | No specific dose adjustment. Use lowest effective dose; monitor for constipation, dehydration, and electrolyte imbalance. Start at 2 mg initially. |
| 1st trimester | Loperamide is generally avoided in the first trimester due to limited safety data; animal studies have shown no teratogenicity but human data are insufficient. Use only if clearly needed. |
| 2nd trimester | Loperamide is considered relatively safe in the second trimester; no evidence of fetal harm, but use caution and only if benefit outweighs risk. |
| 3rd trimester | Loperamide is relatively safe in the third trimester; however, prolonged use may cause maternal constipation and potential fetal effects from decreased gut motility. |
Clinical note
Comprehensive clinical and safety monograph for IMODIUM (IMODIUM).
| Placental transfer | Loperamide crosses the placenta in limited amounts; studies show low transfer (approximately 0.03% of maternal dose) due to high protein binding and low lipophilicity. |
| Breastfeeding | Loperamide is excreted into breast milk in minimal amounts (estimated infant dose <2% of maternal weight-adjusted dose). It is generally considered compatible with breastfeeding, but caution is advised with prolonged high doses due to potential for infant constipation or abdominal discomfort. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to loperamide or any componentAbdominal pain with no known causeAcute dysentery with blood in stool and high feverAcute ulcerative colitisBacterial enterocolitis due to invasive organismsPseudomembranous colitisObstipation or ileusChildren under 2 years of age
| Precautions | Risk of QT prolongation and torsades de pointes, especially with higher doses or in patients with cardiac disease, Use caution in hepatic impairment due to first-pass metabolism, Avoid use if bloody diarrhea or fever present, Risk of toxic megacolon in patients with active ulcerative colitis, Do not use for more than 2 days unless directed by a physician, Use caution in patients with history of opioid dependence or abuse |
| Food/Dietary | Grapefruit juice may increase loperamide absorption and plasma levels, potentially increasing risk of side effects; avoid concurrent intake. High-fiber foods may counteract the antidiarrheal effect and should be minimized during acute episodes. Dairy products may cause diarrhea in lactose-intolerant individuals and can exacerbate symptoms. Avoid large amounts of sorbitol or xylitol (found in sugar-free gums and candies) as they have laxative effects. Caffeine-containing beverages (coffee, tea, soda) may stimulate bowel motility and worsen diarrhea. Spicy and fatty foods can increase gastrointestinal distress. Alcohol can impair gut function and add to CNS depression. |
Loading safety data…
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | FDA Pregnancy Category C. First trimester: Limited human data; animal studies show no teratogenicity at clinically relevant doses but fetal toxicity at high doses. Second and third trimesters: No known fetal risks; may be used if benefit outweighs risk. Avoid prolonged use near term due to potential neonatal respiratory depression and withdrawal symptoms. |
| Fetal Monitoring | Monitor for maternal constipation, abdominal pain, and distension. In prolonged use or high doses, monitor fetal growth and amniotic fluid volume if signs of maternal toxicity. No specific fetal monitoring required for short-term use. |
| Fertility Effects | No significant effects on fertility observed in animal studies. Human data limited; no known impact on conception or spermatogenesis. |
| Clinical Pearls | Loperamide (Imodium) is a peripherally acting mu-opioid receptor agonist that slows gastrointestinal motility and increases fluid absorption. It does not cross the blood-brain barrier at recommended doses due to P-glycoprotein efflux, but excessive dosing can cause CNS depression, especially with concurrent use of P-gp inhibitors like quinidine, verapamil, or amiodarone. Contraindicated in acute dysentery (bloody stools, fever), inflammatory bowel disease exacerbation, and bacterial enterocolitis due to risk of toxic megacolon. Not recommended for children under 2 years. Use with caution in hepatic impairment due to reduced first-pass metabolism. For acute diarrhea, initial dose 4 mg, then 2 mg after each loose stool; maximum 8 mg/day for OTC use (16 mg/day for prescription). For chronic diarrhea (e.g., in irritable bowel syndrome), titrate to control symptoms. May be used for chemotherapy-induced diarrhea, but exclude infectious cause. Consider alternative diagnosis if diarrhea persists >48 hours with treatment. |
| Patient Advice | Take the first dose as 2 tablets (4 mg) for adults, then 1 tablet (2 mg) after each loose stool, but do not exceed 8 mg per day if using over-the-counter, or 16 mg per day if prescribed by a doctor. · Do not use if you have bloody or black stools, mucus in stools, or a fever, as this may indicate a bacterial infection that requires medical attention. · Do not take for more than 2 days without consulting a healthcare provider. If diarrhea persists longer or you have signs of dehydration (dry mouth, dizziness, decreased urination), seek medical advice. · Drink plenty of clear fluids (water, clear broth, oral rehydration solutions) to prevent dehydration. Avoid fruit juices or sugary drinks as they can worsen diarrhea. · Avoid alcohol, caffeine, and spicy or fatty foods as they can irritate the stomach and exacerbate diarrhea. · Do not crush or chew tablets; swallow whole with water. For liquid formulations, use the dosing cup provided. · Do not take more than the recommended dose or combine with other medications containing loperamide. Overdose can cause serious heart problems (irregular heartbeat) or breathing difficulties. · Keep out of reach of children. If overdose occurs, get medical help immediately. · If you are pregnant, breastfeeding, or have liver disease, consult your doctor before use. · Do not use in children under 2 years of age without a doctor's guidance. |