Loperamide (Imodium): Uses, Dosing, Precautions, and Safety
Mechanism
µ-opioid receptor agonist in gut wall → ↓ peristalsis, ↑ water/electrolyte absorption, ↑ anal sphincter tone. Minimal CNS penetration at therapeutic doses (P-glycoprotein efflux).
Indications
- Acute nonspecific diarrhea
- Chronic diarrhea (IBS-D, short bowel, post-cholecystectomy)
- Traveler's diarrhea (adjunct to antibiotics)
- Ileostomy/colostomy output reduction
Dosing
| Population | Initial | Subsequent | Max Daily |
|---|
| Adults | 4 mg | 2 mg after each loose stool | 16 mg (OTC); 8 mg (Rx) |
| Children 6–12 yr | 2 mg (age 6–8) / 2 mg (age 9–12) | 1 mg after each loose stool | 6 mg (6–8 yr) / 8 mg (9–12 yr) |
| Children 2–5 yr | Use only under medical supervision; weight-based | | |
Contraindications & Precautions
- Bloody/mucoid diarrhea, high fever: Possible invasive infection (C. diff, EHEC, Salmonella, Shigella) — loperamide may worsen/toxic megacolon risk
- Acute ulcerative colitis flare: Risk of toxic megacolon
- Liver impairment: Reduced first-pass metabolism → ↑ CNS levels
- Drug interactions: CYP3A4/P-gp inhibitors (itraconazole, clarithromycin, gemfibrozil, quinidine) → ↑ levels; QT-prolonging drugs
- Pregnancy: Category C; avoid unless benefit > risk
Abuse Potential
High doses (>60 mg) cross BBB → opioid euphoria, respiratory depression, cardiac arrhythmia (QT prolongation, torsades). FDA boxed warning. Restricted sales in some jurisdictions.
Side Effects
- Common: constipation, dizziness, nausea, abdominal cramps
- Rare: paralytic ileus, hypersensitivity, pancreatitis
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