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Drug Reference

loperamide

opioid antidiarrheal· Brands: Imodium, Lopex, Diarrhoea ReliefPO

Mechanism of action
Loperamide acts on opioid receptors in the intestinal wall, reducing circular and longitudinal smooth muscle activity, thereby slowing intestinal motility and prolonging transit time. It also increases anal sphincter tone, reducing urgency. It does not cross the blood-brain barrier at therapeutic doses, so has no central analgesic effect.
Pharmacokinetics
Loperamide is poorly absorbed from the gut, with extensive first-pass metabolism by hepatic CYP3A4 and P-glycoprotein. Peak plasma concentrations occur about 2.5 hours after oral administration. It is metabolised primarily in the liver and excreted in faeces as metabolites and unchanged drug. Its half-life is approximately 10 to 12 hours. The drug is mostly confined to the gut due to poor absorption and efflux transport, contributing to its local action.
Indications & dosing

Acute diarrhoea

Initial dose 4 mg, followed by 2 mg after each loose stool. Maximum 16 mg/day. Not recommended for acute dysentery or bloody diarrhoea.

  • adult · PO: 2 mg after each stool · Initial dose 4 mg, followed by 2 mg after each loose stool. Maximum 16 mg/day. Not recommended for acute dysentery or bloody diarrhoea.

Chronic diarrhoea

Titrate to the lowest effective dose; used in conditions such as inflammatory bowel disease or short bowel syndrome.

  • adult · PO: 2–6 mg daily in 2-3 doses · Titrate to the lowest effective dose; used in conditions such as inflammatory bowel disease or short bowel syndrome.

High-output ileostomy

Individualised dosing; monitor fluid and electrolyte balance and stoma output.

  • adult · PO: 2–4 mg up to 3 times daily · Individualised dosing; monitor fluid and electrolyte balance and stoma output.
Contraindications & precautions
  • Acute dysentery (bloody diarrhoea) · May worsen infection by retaining pathogen; use only if specific antibacterial treatment is given.
  • Acute ulcerative colitis · Risk of toxic megacolon and masking of disease exacerbation.
  • Bacterial enterocolitis (e.g., Salmonella, Shigella, Campylobacter) · Avoid as it may delay and mask symptoms, prolonging infection.
  • Pseudomembranous colitis (Clostridioides difficile) · Risk of toxic megacolon and worsening of diarrhoea.
  • Obstipation or abdominal distension · Use contraindicated in the presence of intestinal obstruction or severe abdominal pain.
  • Children under 2 years · Not recommended due to risk of serious adverse effects.
  • Avoid in acute diarrhoea with high fever, severe abdominal pain, or bloody diarrhoea; investigate underlying cause first.
  • Use with caution in hepatic impairment; reduce dose or avoid in severe liver disease.
  • Do not exceed recommended doses; risk of QT prolongation and respiratory depression with overdose.
  • In patients with AIDS and diarrhoea with abdominal distension, use caution and monitor for toxic megacolon.
  • Drug interactions: P-glycoprotein inhibitors (e.g., quinidine) or CYP3A4 inhibitors can increase loperamide levels; monitor for toxicity.
Adverse effects
  • Constipation
  • Dry mouth
  • Abdominal cramps or discomfort
  • Nausea
  • Dizziness
  • Drowsiness or fatigue
  • Ileus or paralytic ileusserious
  • Toxic megacolonserious
  • QT prolongation with overdose or high dosesserious
  • Angioedema or anaphylaxisserious
Renal & hepatic adjustment
  • eGFR 0+: No adjustment required. Use caution in severe renal impairment.
  • Hepatic impairment (mild): No dose adjustment required. Use with caution.
  • Hepatic impairment (moderate): Consider dose reduction and monitor for adverse effects.
  • Hepatic impairment (severe): Avoid use due to risk of overdose and encephalopathy. (avoid)
Monitoring, pregnancy & toxicity
  • Bowel frequency and consistency · During therapy
  • Signs of CNS depression and respiratory depression · In overdose or in children
  • Signs of dehydration · If diarrhoea persists
  • Pregnancy: Loperamide may be used during pregnancy if clinically needed. Data are limited but show no clear association with fetal harm. Consult a specialist if prolonged use.
  • Toxicity: CNS depression and respiratory depression · Administer naloxone; supportive care.
  • Toxicity: Cardiac toxicity (QT prolongation, ventricular arrhythmias) in large doses · Monitor ECG; correct electrolytes; administer activated charcoal if within 2 hours; consider antiarrhythmic therapy.
  • Toxicity: Paralytic ileus and severe constipation · Discontinue use; give laxatives or enemas; consider rectal or surgical intervention.
  • Toxicity: Hypotension · IV fluids and vasopressors if needed.
Clinical notes
Loperamide is indicated for symptomatic relief of acute diarrhoea and chronic diarrhoea associated with inflammatory bowel disease. It is also used to reduce ileostomy output. The usual adult dose is 4 mg initially, followed by 2 mg after each loose stool, up to a maximum of 16 mg daily for acute diarrhoea; for chronic diarrhoea, doses are adjusted individually. It is contraindicated in acute ulcerative colitis, pseudomembranous colitis, and bacterial enterocolitis. Caution in hepatic impairment, children, and pregnancy. Not recommended for use as a single agent in acute dysentery or with a fever. Overdose can cause constipation and central nervous system effects, although naloxone may be needed in severe cases.

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BNF; local formulary