What it does
Lactulose is a type of sugar used to treat constipation and help with liver problems.
Commonly used for: constipation, hepatic encephalopathy
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Source: Pharmacy and Medicines Regulatory Authority · fetched 2026-04-21 17:37:44 · updated 2026-09-29 04:33:06
About this medicine
Lactulose is a type of sugar used to treat constipation and help with liver problems.
What it treats
- constipation
- hepatic encephalopathy
How it works
Lactulose works by drawing water into the bowel, which makes it easier to pass stool.
Who it's for
Lactulose is for adults and children who need help with constipation or have certain liver issues.
Cautions
- • May cause bloating or gas.
- • Should be used with care in people with diabetes.
AI-assisted summary grounded in BNF data - general information only, not medical advice. Always confirm with your pharmacist or doctor.
Clinical monograph: lactilose
Lactulose is a synthetic disaccharide that is primarily used as a laxative for the treatment of constipation and hepatic encephalopathy. It works by drawing water into the bowel, increasing stool volume and promoting bowel movements. Lactulose is not absorbed in the gastrointestinal tract, which makes it effective for its intended uses.
Indications
- Constipation
- Hepatic encephalopathy
Dosage
Children: For paediatric dosing, refer to the BNF for Children for specific recommendations based on age and weight.
Adults: The usual adult dose for constipation is 15 to 30 ml daily, which may be adjusted based on response. For hepatic encephalopathy, the usual dose starts at 30 to 50 ml three times daily, which can be adjusted to achieve 2 to 3 soft stools per day.
Mechanism of action
Lactulose is metabolized by colonic bacteria into short-chain fatty acids, which lowers the pH of the colonic contents. This acidic environment leads to increased osmotic pressure, promoting the retention of water in the colon and facilitating bowel movements. In hepatic encephalopathy, lactulose reduces ammonia absorption from the gut by converting ammonia into ammonium, which cannot cross the intestinal membrane.
Pharmacodynamics
Lactulose acts as an osmotic laxative, enhancing the water content of the stool, which softens it and increases its bulk. This promotes peristalsis and leads to the evacuation of the bowels. In the context of hepatic encephalopathy, it reduces the absorption of ammonia and helps to prevent the accumulation of toxins that can affect brain function.
Pharmacokinetics
Lactulose is not absorbed in the gastrointestinal tract and therefore has no systemic bioavailability. It is fermented in the colon by bacteria, which produces organic acids. The effects of lactulose are primarily local in the gastrointestinal tract. Its onset of action generally occurs within 24 to 48 hours after ingestion.
Contra-indications
- Galactosemia
- Severe abdominal pain
- Bowel obstruction
Adverse effects
- Diarrhea
- Abdominal cramps
- Flatulence
- Nausea
- Dehydration
Interactions
- May decrease the absorption of other oral medications due to increased gastrointestinal motility
- Caution with concomitant use of other laxatives
Precautions
- Use with caution in patients with diabetes mellitus due to potential carbohydrate content
- Monitor electrolytes in patients with prolonged use
- Assess renal function in patients with existing renal impairment
Pregnancy
Lactulose is generally considered safe in pregnancy, but it should be used under medical supervision.
Breast-feeding
Lactulose is excreted in breast milk but is not expected to harm a nursing infant.
Storage
Store at room temperature, away from light and moisture. Keep out of reach of children.
Formulations
- Oral solution
- Syrup
AI-synthesized from BNF references - general information only, not a substitute for professional medical advice or the current BNF. Verify doses with a pharmacist.