IMODIUM A-D
Clinical safety rating: caution
Comprehensive clinical and safety monograph for IMODIUM A-D (IMODIUM A-D).
Loperamide is a synthetic piperidine derivative that acts as an agonist at mu-opioid receptors in the myenteric plexus of the gastrointestinal tract. It inhibits peristalsis by decreasing circular and longitudinal smooth muscle activity, prolonging gastrointestinal transit time, and increasing water and electrolyte absorption. It also increases anal sphincter tone, reducing fecal urgency and incontinence. Loperamide has poor bioavailability and does not cross the blood-brain barrier significantly at therapeutic doses, limiting central opioid effects.
| Metabolism | Loperamide is extensively metabolized in the liver, primarily via CYP2C8 and CYP3A4, with minor contribution from CYP2B6 and CYP2D6. It undergoes N-demethylation to form N-desmethylloperamide, which is further metabolized. The drug and its metabolites are excreted predominantly in feces via biliary elimination (approximately 97%), with less than 2% excreted renally. Enterohepatic recirculation contributes to prolonged duration of action. |
| Excretion | Primarily fecal (approximately 95% as unchanged drug and metabolites) with minimal renal excretion (<1% unchanged). |
| Half-life | Terminal elimination half-life is approximately 9-14 hours (mean 11.2 hours) in patients with diarrhea; clinical significance: steady-state achieved within 2-4 days. |
| Protein binding | Approximately 97% bound to plasma proteins, primarily to albumin. |
| Volume of Distribution | Volume of distribution is approximately 1.4-2.6 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 40% (range 20-60%) due to extensive first-pass metabolism; bioavailability of the capsule formulation is similar to tablet. |
| Onset of Action | Oral: onset of antidiarrheal effect within 1-3 hours. |
| Duration of Action | Duration of antidiarrheal effect is approximately 8-12 hours (up to 24 hours in some patients); effect may persist longer than capsule due to enteric coating. |
| Molecular Weight | 513.5 |
4 mg orally initially, then 2 mg after each unformed stool; maximum 8 mg/day for OTC use; 16 mg/day for prescription use. Duration not to exceed 2 days.
| Dosage form | SOLUTION |
| Renal impairment | No dosage adjustment required for renal impairment; use with caution in severe impairment due to potential accumulation of metabolites. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: avoid use due to risk of encephalopathy. |
| Pediatric use | Age 2-5 years: 1 mg orally three times daily (max 3 mg/day); Age 6-8 years: 2 mg orally twice daily (max 4 mg/day); Age 9-11 years: 2 mg orally three times daily (max 6 mg/day); Weight-based: 0.08-0.24 mg/kg/day in divided doses. |
| Geriatric use | Initiate at the lower end of dosing range due to decreased hepatic and renal function; maximum 8 mg/day; monitor for constipation and ileus. |
| 1st trimester | Animal studies have shown no evidence of teratogenicity. Insufficient human data; use only if clearly needed. |
| 2nd trimester | No known risk in animal studies; limited human data. Use with caution. |
| 3rd trimester | Avoid use in third trimester due to potential for gastrointestinal effects in neonate (case reports of constipation). |
Clinical note
Comprehensive clinical and safety monograph for IMODIUM A-D (IMODIUM A-D).
| Placental transfer | Loperamide crosses the placenta minimally (<5% of maternal plasma concentration). Animal studies show low transfer; human data limited but suggest minimal fetal exposure. |
| Breastfeeding | Loperamide is excreted into breast milk in low concentrations (milk:plasma ratio ~0.4). Short-term use of low doses is likely compatible, but prolonged high doses may cause infant constipation or poor feeding. Monitor infant for sedation, constipation, or poor weight gain. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to loperamide or any componentAcute dysentery (bloody stools, high fever)Acute ulcerative colitisPseudomembranous colitisBacterial enterocolitisObstructive ileusAbdominal pain of unknown origin (e.g., appendicitis)
| Precautions | Risk of cardiac arrhythmias (QT prolongation, torsade de pointes, cardiac arrest) with high doses or overdose, especially in patients with underlying cardiac conditions, electrolyte disturbances, or concurrent use of QT-prolonging drugs., Potential for abuse and misuse leading to serious adverse effects, including respiratory depression and opioid withdrawal in physically dependent individuals., Caution in patients with hepatic impairment due to reduced first-pass metabolism, leading to increased systemic exposure and risk of toxicity., Use should be discontinued promptly if constipation, abdominal distention, or ileus develop., Not recommended for use in acute dysentery (bloody stools, high fever), patients with active inflammatory bowel disease (acute ulcerative colitis), or bacterial enterocolitis due to risk of toxic megacolon., May mask symptoms of underlying infectious diarrhea and delay diagnosis., Use in children under 6 years of age is not recommended due to increased susceptibility to adverse effects; doses must be carefully weight-based in pediatric patients. |
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| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Loperamide is generally considered low risk during pregnancy based on limited human data; animal studies have not shown teratogenicity. FDA Pregnancy Category C. No evidence of increased risk of major malformations in first trimester; however, high doses or prolonged use in third trimester may be associated with neonatal withdrawal symptoms such as irritability and feeding difficulties. |
| Fetal Monitoring | During pregnancy, monitor for signs of constipation and abdominal distention; avoid prolonged use. In third trimester, monitor fetal movements and maternal bowel function. No specific fetal monitoring required unless high doses or prolonged therapy is used. |
| Fertility Effects | Loperamide has no known significant effects on human fertility. Animal studies have not shown impaired fertility at clinically relevant doses. Caution in women attempting conception only if chronic use may affect ovulation indirectly via gastrointestinal motility changes. |
| Food/Dietary | Grapefruit juice may increase loperamide levels via CYP3A4 inhibition; avoid concurrent consumption. Alcohol can exacerbate drowsiness or dizziness. No specific dietary restrictions; maintain hydration with clear liquids (water, broth, electrolyte solutions). Avoid dairy products if lactose intolerance is suspected. |
| Clinical Pearls | Loperamide is a peripherally acting mu-opioid receptor agonist that slows gastrointestinal motility and increases fluid and electrolyte absorption. It does not cross the blood-brain barrier significantly at usual doses, minimizing central opioid effects. Onset of action is within 1 hour; duration is 4-6 hours. Maximum dose for self-treatment is 8 mg/day; for medical supervision, up to 16 mg/day. Contraindicated in acute dysentery (bloody stools), inflammatory bowel disease, or suspected bacterial enterocolitis due to risk of toxic megacolon. Coadministration with CYP3A4 inhibitors (e.g., macrolides, antifungals) or P-gp inhibitors (e.g., verapamil) can increase loperamide levels, risking cardiotoxicity (QT prolongation, Torsades de Pointes). |
| Patient Advice | Take as directed; do not exceed 8 mg in 24 hours unless under medical advice. · Discontinue use if diarrhea persists for more than 2 days or if symptoms worsen. · Stop immediately and seek medical attention if you develop fever, bloody stools, or severe abdominal pain. · Drink plenty of clear fluids to prevent dehydration. · Do not use with other opioid medications due to risk of increased side effects. · Store at room temperature away from moisture and heat. |