Laxatives · Gastrointestinal
Lactulose
Duphalac® · Lactulax®(brand names vary by market)
An osmotic laxative that doubles as an ammonia trap.
Mechanism
A non-absorbable disaccharide fermented by colonic bacteria into short-chain acids. Those acids draw in water and acidify the lumen, converting ammonia to ammonium, which cannot cross back into the blood.
Indications
- Hepatic encephalopathy, treatment and prevention
- Constipation
Formulations
Dosing concepts
Titrated to stools, not to millilitres
In encephalopathy the target is two to three soft stools daily. That is the dose instruction, and it is what the family should be told.
Rectal route
Given as an enema when a patient is too encephalopathic to swallow safely.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- Not absorbed
- Half-life
- Acts within 24 to 48 h orally, faster rectally
- Elimination
- plasma: Fermented and excreted in stool
Adverse effects
- Flatulence and bloatingcommonThe fermentation that makes it work is also what makes it uncomfortable.
- Crampingcommon
- Dehydration and hypernatremia with over-treatmentseriousExcessive diarrhoea can precipitate the very encephalopathy it is treating.
- Nausea from the sweet tastecommon
Contraindications & precautions
Contraindications
- Galactosemia
- Bowel obstruction
Precautions
- Diabetes, given the sugar content
- Over-treatment producing volume depletion
Interactions
No curated interaction entries yet for this agent.
Monitoring
Number and consistency of stools daily
The actual dosing target in encephalopathy
Mental state
The clinical endpoint
Sodium and volume status
Over-treatment causes harm in both directions
Counselling points
- The aim is two to three soft stools a day. Adjust the dose to reach that.
- Wind and bloating are common at first.
- If you or your family notice confusion returning, tell us: the dose may need adjusting.
- Too many stools is also a problem; do not push through it.
Clinical pearls
- The dose is written as a stool target rather than a volume, and teaching the family that single fact prevents a large share of encephalopathy readmissions.
- Ammonia levels correlate poorly with the clinical picture; treatment is titrated against mental state and stools, not against the number.
References & review
- Lactulose product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.