Osmotic laxative / Ammonia reduction (hepatic encephalopathy) Pregnancy: May be used during pregnancy if necessary (limited data indicate no malformative or foeto/neonatal toxicity). Can be used during breast-feeding.

Lactulose

Brand names: Lactulose, Duphalac

Used in: Liver Disease & Cirrhosis

Lactulose is an osmotic laxative used for constipation and for the treatment and prevention of hepatic encephalopathy.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting dose 15-45 ml daily (10-30 g lactulose); maintenance dose 15-30 ml daily (10-20 g lactulose)

Route: Oral (may be given diluted or undiluted; swallow in one and do not hold in the mouth)

Frequency: As a single daily dose (e.g. at breakfast) or in 2-3 divided doses; titrate to clinical response

For constipation. Titrate to individual response; 2-3 days of treatment may be needed before adequate effect. Drink sufficient fluid (1.5-2 L/day). Reduce the dose if diarrhoea occurs. Elderly, and patients with renal or hepatic impairment: no special dosage recommendations. Paediatric bands (SPC): adolescents over 14 years — as adults (start 15-45 ml, maintenance 15-30 ml); children 7-14 years — 15 ml daily (10 g) for both starting and maintenance; for infants, toddlers and children up to 6 years use the bottle presentation for precise dosing. Use of laxatives in children should be exceptional and under medical supervision.

Dose adjustments

Renal

No special dosage recommendations in renal impairment (or in hepatic impairment).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION Oral Adult: The usual adult, oral dosage is 2 to 3 tablespoonfuls (30 to 45 ml, containing 20 g to 30 g of lactulose) three or four times daily. The dosage may be adjusted every day or two to produce 2 or 3 soft stools daily. Hourly doses of 30 to 45 ml of Lactulose may be used to induce the rapid laxation indicated in the initial phase of the therapy of portal-systemic encephalopathy. When the laxative effect has been achieved, the dose of lactulose may then be reduced to the recommended daily dose. Improvement in the patient's condition may occur within 24 hours but may not begin before 48 hours or even later. Continuous long-term therapy is indicated to lessen …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2022-06-01. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Galactosaemia
Acute inflammatory bowel disease (ulcerative colitis, Crohn's disease)
Gastrointestinal obstruction or subocclusive syndromes
Digestive perforation or risk of digestive perforation
Painful abdominal syndromes of undetermined cause

Side effects

Flatulence (very common; usually settles after a few days)
Abdominal pain (very common)
Nausea and vomiting (common)
Diarrhoea if dosed too high (may include electrolyte imbalance)
Not known: hypersensitivity reactions, rash, pruritus, urticaria

Interactions

May increase the potassium loss caused by other drugs (e.g. thiazides, corticosteroids, amphotericin B)
Cardiac glycosides — effect may be increased through lactulose-induced potassium deficiency
Colonic pH-dependent release drugs (e.g. 5-ASA / mesalazine) may be inactivated by the lower colonic pH

Clinical monograph

How it works

A non-absorbed disaccharide that osmotically draws water into the bowel; in hepatic encephalopathy it also acidifies the colon and reduces ammonia absorption.

Prescribing in practice

For constipation it may take a day or two to work and commonly causes flatulence and cramps initially.
Avoid in galactosaemia and intestinal obstruction.
In hepatic encephalopathy the dose is titrated to achieve a target number of soft stools per day.

Monitoring

Review bowel habit; in hepatic encephalopathy titrate to the target stool frequency and monitor mental state.

Counselling the patient

It can take 1-2 days to work.
Some bloating or wind is common at first and usually settles.
Keep up your fluid intake.

Evidence & guidelines

A first-line osmotic laxative for constipation and standard therapy in hepatic encephalopathy.

Reference: EASL HE Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways