LOPERAMIDE HYDROCHLORIDE
Clinical safety rating: safe
QT prolongation has been reported with high doses Can cause toxic megacolon in patients with infectious diarrhea.
Loperamide binds to µ-opioid receptors in the intestinal wall, reducing propulsive peristalsis and increasing intestinal transit time. It also inhibits calcium-calmodulin-dependent pathways, decreasing electrolyte and water secretion, and enhances anal sphincter tone.
| Metabolism | Primarily metabolized by CYP2C8 and CYP3A4 to N-desmethylloperamide; also O-demethylation via CYP2D6. Extensive first-pass metabolism. |
| Excretion | Primarily fecal (30-40% as unchanged drug, 50-60% as metabolites); renal excretion accounts for <5% of unchanged drug and ~10% of metabolites. |
| Half-life | Terminal elimination half-life is 9-14 hours (mean 10.8 hours) in adults; may be prolonged in hepatic impairment. |
| Protein binding | Approximately 95-97% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 9-20 L/kg (mean 14 L/kg), indicating extensive extravascular distribution. |
| Bioavailability | Oral bioavailability is approximately 40-60% due to extensive first-pass metabolism (primarily N-dealkylation via CYP3A4 and CYP2C8). |
| Onset of Action | Oral: 0.5-1 hour (tablets) or 0.5-2 hours (liquid); onset is faster with liquid formulation. |
| Duration of Action | Antidiarrheal effect lasts 4-6 hours after a single dose; maximal effect at 2-3 hours; duration may be longer with higher doses. |
| Molecular Weight | 513.51 |
4 mg orally initially, followed by 2 mg after each unformed stool; maximum 16 mg per day. For chronic diarrhea, 4 mg orally once, then 2 mg after each unformed stool until diarrhea controlled; typical maintenance 4-8 mg daily in divided doses. Traveler's diarrhea: 4 mg initially, then 2 mg after each loose stool; maximum 8 mg per day for up to 2 days.
| Dosage form | CAPSULE |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. For severe renal impairment (GFR < 30 mL/min), use with caution due to potential accumulation; consider dose reduction or extended interval. No specific GFR-based guidelines available; clinical monitoring advised. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B: Reduce dose by 50% or extend interval; maximum 8 mg/day. Child-Pugh Class C: Avoid use or use with extreme caution; maximum 6 mg/day with close monitoring for CNS toxicity. Loperamide is hepatically metabolized; accumulation may occur. |
| Pediatric use | Children 2-5 years (13-20 kg): 1 mg orally three times daily (maximum 3 mg/day). 6-8 years (20-30 kg): 2 mg orally twice daily (maximum 4 mg/day). 8-12 years (>30 kg): 2 mg orally three times daily (maximum 6 mg/day). For acute diarrhea: initial dose based on weight, then 0.1 mg/kg after each unformed stool; not to exceed initial dose per 24 hours. Use only under medical supervision; contraindicated in children <2 years. |
| 1st trimester | Animal studies have not shown evidence of teratogenicity. No well-controlled studies in pregnant women. Use only if clearly needed and potential benefit justifies risk. |
| 2nd trimester | Same as T1. Generally considered safe for short-term use. |
| 3rd trimester | Avoid use near term due to potential risk of neonatal opioid-like effects (e.g., respiratory depression, constipation) if used in high doses or for prolonged periods. |
Clinical note
QT prolongation has been reported with high doses Can cause toxic megacolon in patients with infectious diarrhea.
| FDA category | Animal |
| Placental transfer | Limited data suggest minimal placental transfer. Animal studies indicate low passage; human data are scarce but imply transfer is negligible. |
■ FDA Black Box Warning
None.
| Common Effects | Constipation |
| Serious Effects |
Hypersensitivity to loperamide or any componentAcute dysentery (bloody stools, high fever)Acute ulcerative colitisPseudomembranous colitisBacterial enterocolitis caused by invasive organisms including Salmonella, Shigella, and CampylobacterAbdominal pain without diarrheaChildren <2 years of age
| Precautions | Do not use for diarrhea with high fever or bloody stools (risk of bacterial enterocolitis), Prolonged use may lead to constipation and toxic megacolon in IBD, Avoid use in children <2 years due to risk of respiratory depression, Risk of cardiac arrhythmias (QT prolongation, Torsades de Pointes) with high doses or when combined with drugs inhibiting CYP3A4 or P-glycoprotein, Dehydration and electrolyte imbalances should be corrected before use |
| Food/Dietary |
Loading safety data…
| Geriatric use |
| Initiate at lower doses (e.g., 2 mg initially) due to increased sensitivity and risk of CNS effects, constipation, and dehydration. Monitor for electrolyte imbalances and prolonged QT interval. Maximum 8 mg/day for acute diarrhea; adjust based on response and tolerability. Avoid in patients with advanced age and multiple comorbidities unless necessary. |
| Breastfeeding |
| Loperamide is excreted into breast milk in low concentrations. Single doses are considered compatible with breastfeeding. However, avoid prolonged or high-dose use due to potential for infant effects (e.g., drowsiness, constipation). Monitor infant for signs of sedation. |
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | Loperamide hydrochloride is classified as FDA Pregnancy Category C. Animal studies have shown no evidence of teratogenicity at doses up to 40 mg/kg/day in rats (maternal toxic doses). In humans, data from postmarketing reports and small studies suggest no increased risk of major malformations after first-trimester exposure, but there is insufficient data for second and third trimesters. Potential for neonatal opioid withdrawal syndrome if used near term. |
| Fetal Monitoring | No specific maternal-fetal monitoring is routinely required. However, in pregnant women, monitor for signs of constipation, ileus, or CNS depression, especially with prolonged use. Fetal monitoring is not indicated unless maternal adverse effects occur. For neonates, monitor for signs of opioid withdrawal if loperamide was used near term. |
| Fertility Effects | Preclinical studies in animals at high doses (40 mg/kg/day) showed no effects on fertility or reproductive performance. In humans, there are no controlled studies; however, due to minimal systemic absorption and short-term use, loperamide is not expected to impair fertility. Chronic high-dose use might theoretically affect male or female reproductive function via opioid receptor activity, but clinical evidence is lacking. |
| Avoid grapefruit juice as it may increase loperamide absorption and risk of side effects. Take loperamide on an empty stomach or with a small amount of food if gastrointestinal upset occurs, but food may delay onset of action. No other significant food interactions. |
| Clinical Pearls | Loperamide is an opioid receptor agonist that acts on μ-opioid receptors in the gut to decrease peristalsis and increase fluid reabsorption. It does not cross the blood-brain barrier at therapeutic doses due to P-glycoprotein efflux, making it non- analgesic and non-addictive. However, high doses (e.g., >16 mg/day) can overcome P-glycoprotein, leading to CNS effects (e.g., respiratory depression). Avoid use in acute dysentery (bloody stools, fever) due to risk of toxic megacolon. Monitor for constipation and abdominal distension, especially in elderly or patients with inflammatory bowel disease. Not recommended for children under 2 years. |
| Patient Advice | Take loperamide only for diarrhea, not for other conditions · Do not exceed 8 mg per day for self-treatment; for chronic diarrhea, follow your doctor's dosing · Drink plenty of clear fluids to prevent dehydration · Stop taking loperamide and contact your doctor if you have bloody stools, fever, or worsening abdominal pain · Avoid alcohol while taking loperamide as it may increase side effects · Loperamide may cause dizziness or drowsiness; avoid driving until you know how it affects you · Keep out of reach of children; accidental overdose can cause serious breathing problems |