Osmotic laxative / Ammonia reduction (hepatic encephalopathy) Pregnancy: Safe in pregnancy for constipation.

Lactulose

Brand names: Lactulose, Duphalac

Adult dose

Dose: Constipation: 15 mL twice daily; Hepatic encephalopathy: 30–50 mL three times daily (titrate to 2–3 soft stools/day)

Route: Oral

Frequency: Twice daily (constipation); three times daily (hepatic encephalopathy)

Max: 150 mL/day (hepatic encephalopathy)

Constipation: 15 mL BD, increase to 30 mL BD if needed (onset 24–48 hours). Hepatic encephalopathy: 30–50 mL TDS (titrate to 2–3 soft stools per day to reduce ammonia absorption). Can dilute in water/juice if too sweet. For rectal use: 300 mL in 700 mL water as enema.

Paediatric dose

Route: Oral

Frequency: Twice daily

Max: 30 mL twice daily (adolescents)

1–5 years: 2.5 mL BD. 5–10 years: 5 mL BD. 10–17 years: 10–15 mL BD. Chronic constipation: adjust to produce 1–2 soft stools daily.

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Indicated FOR hepatic impairment (hepatic encephalopathy).

Clinical pearls

Onset 24–48 hours — counsel patient accordingly
Mechanism (HE): decreases gut pH, reduces ammonia-producing bacteria, traps ammonium ions
In hepatic encephalopathy, titrate dose to 2–3 soft stools/day
Excessive doses cause diarrhoea and electrolyte disturbances — monitor in elderly
Macrogol (polyethylene glycol) equally effective for constipation with less flatulence

Contraindications

Galactosaemia
Intestinal obstruction

Side effects

Flatulence and bloating
Abdominal cramps
Diarrhoea (excessive doses)
Hypernatraemia (excessive doses in elderly with poor fluid intake)
Electrolyte disturbances (excessive use)

Interactions

Antacids — may reduce lactulose efficacy
Antibiotics (neomycin, metronidazole) — also used for hepatic encephalopathy (additive)

Monitoring

Stool frequency and consistency
Electrolytes (prolonged use in elderly)
Ammonia level (HE indication)

Reference: BNFc; BNF; BNFc; EASL HE Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways