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. |
| 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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for IMODIUM (IMODIUM).
| Breastfeeding | Loperamide is excreted into human breast milk in low amounts. M/P ratio is approximately 0.5-0.7. Due to low milk concentrations, it is considered compatible with breastfeeding. Use caution with high doses or prolonged use; monitor infant for constipation or drowsiness. |
| 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. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to loperamide or any component","Children less than 2 years of age","Acute dysentery (bloody stool, high fever)","Active ulcerative colitis","Bacterial enterocolitis","Pseudomembranous colitis (e.g., Clostridium difficile)","Obstructive ileus or abdominal distention"]
| 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"] |
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| 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. |