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Osmotic Laxative / Ammonia-Reducing Agent Pregnancy: Section 4.6: no effects during pregnancy are anticipated, since systemic exposure to lactulose is negligible, and the SPC states plainly that 'Duphalac can be used during pregnancy'. Breast-feeding: no effects on the breastfed newborn or infant are anticipated for the same reason, and 'Duphalac can be used during breast-feeding'. Fertility: no effects are to be expected.

Lactulose (Hepatic Encephalopathy)

Brand names: Duphalac

This is the use of lactulose, an osmotic disaccharide laxative, as first-line treatment and prophylaxis of hepatic encephalopathy in patients with chronic liver disease.

Adult dose

Dose: Hepatic encephalopathy, adults. Starting dose 30-45 ml per dose (6-9 x 5 ml spoonfuls, or 2-3 of the 15 ml single-dose sachets), given 3 to 4 times daily. This is then adjusted to a maintenance dose that achieves two or three soft stools each day. Oral route only — this SPC gives no rectal/enema and no nasogastric regimen, so the rectal route this page also lists is not dosed here.
Route: Oral. Duphalac 3.335 g/5 ml oral solution, given diluted or undiluted; each dose may be taken with water or fruit juice, should be swallowed in one, and should not be kept in the mouth for an extended period. For lactulose in bottles the measuring cup may be used; for 15 ml single-dose sachets, tear off the corner and take the contents immediately.
Frequency: 3 to 4 times daily at the starting dose, then titrated to the maintenance dose that produces two or three soft stools each day.
Max: 45 ml per dose, given up to 4 times daily — the top of the starting-dose range this SPC states for hepatic encephalopathy. The label sets no separate daily-total ceiling for this indication; instead the dose is titrated DOWN from the starting dose to the maintenance dose once two or three soft stools a day are achieved.
VERBATIM section 4.2, hepatic encephalopathy: 'Dosing in Hepatic Encephalopathy Adults Starting dose : 3 to 4 times daily 30-45 ml (6-9 x 5 ml spoonfuls) or 2-3 sachets. This dose may be adjusted to the maintenance dose to achieve two or three soft stools each day.' The endpoint is the stool count, not a fixed millilitre figure. || The SPC's own range is 30-45 ml per dose. || A DIFFERENT INDICATION, QUOTED ONLY SO IT IS NOT CONFUSED WITH THE ABOVE — constipation, which is dosed far lower: adults and adolescents, starting dose 15-45 ml daily (1-3 sachets), maintenance 15-30 ml daily (1-2 sachets), given as a single daily dose or in two divided doses, with several days (2-3 days) of treatment possibly needed before effect. Note the units differ in kind: the constipation figures are DAILY totals, the hepatic encephalopathy figures are PER-DOSE amounts repeated 3 to 4 times a day. Do not read one as the other. || DIABETICS: section 4.4 verbatim — 'The dose normally used in constipation should not pose a problem for diabetics. The dose used in the treatment of HE is usually much higher and may need to be taken into consideration for diabetics.' || GENERAL: the posology should be adjusted according to the individual needs of the patient; in the case of a single daily dose it should be taken at the same time each day, e.g. during breakfast; during laxative therapy it is recommended to drink sufficient fluids (1.5-2 litres, equal to 6-8 glasses) during the day. || ELDERLY, RENAL AND HEPATIC IMPAIRMENT: 'No special dosage recommendations exist, since systemic exposure to lactulose is negligible.' No adjustment is required for the liver disease that underlies the indication itself. || PAEDIATRIC — NOT DOSED FOR THIS INDICATION, AND THE LABEL SAYS SO EXPLICITLY. Section 4.2 verbatim: 'Paediatric population The safety and efficacy in children (newborn to 18 years of age) with HE have not been established. No data are available.' paedDose is therefore null. The paediatric figures that do appear in this SPC (children 7-14 years 15 ml starting / 10-15 ml maintenance daily; children 1-6 years 5-10 ml daily; infants under 1 year up to 5 ml daily) belong to the CONSTIPATION table, a different indication, and must not be carried onto this hepatic encephalopathy page. Section 4.4 adds that 'Use of laxatives in children should be exceptional and under medical supervision', and section 4.2 that for precise dosing in infants and children up to 7 years, lactulose in bottles should be used.

Dose adjustments

Renal

None required. Section 4.2 verbatim, for elderly patients and patients with renal or hepatic insufficiency: 'No special dosage recommendations exist, since systemic exposure to lactulose is negligible.'

Hepatic

None required, including in the advanced liver disease that gives rise to this indication. Section 4.2 verbatim: 'No special dosage recommendations exist, since systemic exposure to lactulose is negligible.' The dose is titrated to the stool count rather than to liver function.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or any of the excipients listed in section 6.1
  • Galactosaemia
  • Gastro-intestinal obstruction, perforation or risk of perforation
  • Not a formal contraindication but an exclusion in section 4.4: this product contains lactose, galactose and fructose from the route of production, so patients with rare hereditary problems of galactose or fructose intolerance, total lactase deficiency or glucose-galactose malabsorption should not take it; it also contains sulphite, and should be administered with care to patients intolerant of lactose
  • PROVENANCE: section 4.3 of the Duphalac 3.335 g/5 ml Oral Solution SPC, complete in the bundle, plus the excipient exclusion from section 4.4.

Side effects

  • Very common: diarrhoea
  • Common: flatulence, abdominal pain, nausea, vomiting
  • Flatulence may occur during the first few days of treatment; as a rule it disappears after a couple of days
  • Electrolyte imbalance due to diarrhoea — specifically flagged for this indication: if high doses (normally only associated with hepatic encephalopathy) are used for an extended period, the patient may experience electrolyte imbalance due to diarrhoea, and the dosage should then be adjusted to obtain two or three formed stools per day
  • Abdominal pain and diarrhoea when dosages higher than instructed are used — in that case the dosage should be decreased
  • Hypersensitivity reactions
  • Rash, pruritus and urticaria (post-marketing experience)
  • Chronic use of unadjusted doses and misuse can lead to diarrhoea and disturbance of the electrolyte balance; the defaecation reflex could be disturbed during treatment
  • FREQUENCY CAVEAT AND PROVENANCE: section 4.8 of the Duphalac SPC, which is complete in the bundle. Only diarrhoea (very common) and the four other gastrointestinal reactions (common) sit unambiguously in their frequency columns; the electrolyte, immune and skin rows did not survive the fetch as aligned columns, so no band is asserted for those. The safety profile in children is expected to be similar to adults.

Monitoring

  • Stool count is the therapeutic endpoint — titrate the dose to two or three soft stools each day, and adjust to two or three FORMED stools per day if prolonged high-dose therapy causes electrolyte imbalance through diarrhoea
  • Electrolyte balance during prolonged treatment at the high doses used in hepatic encephalopathy
  • Blood glucose in diabetics: the dose used in hepatic encephalopathy is usually much higher than the constipation dose and may need to be taken into consideration
  • Reconsider the dose and/or additional measures if there is insufficient therapeutic effect after several days
  • Before starting, evaluate painful abdominal symptoms of undetermined cause to exclude undiagnosed perforation or obstruction, or an undiagnosed condition that predisposes to either
  • Fluid intake — 1.5-2 litres (6-8 glasses) a day is recommended during laxative therapy
  • Section 4.5 states that no interaction studies have been performed

Clinical monograph

How it works

Colonic fermentation of lactulose acidifies the bowel contents, which traps ammonia as ammonium and reduces its absorption while increasing gut transit, thereby lowering blood ammonia and the nitrogenous load driving encephalopathy.

Prescribing in practice

  • Titrate the dose to achieve the target of a small number of soft stools each day, as this is the therapeutic endpoint in encephalopathy rather than simply relieving constipation.
  • Excessive use can cause diarrhoea with dehydration and electrolyte disturbance, which may itself precipitate or worsen encephalopathy, so balance is essential.
  • It may be given by mouth or, in patients unable to swallow safely, rectally, and is often combined with rifaximin for recurrent episodes.

Monitoring

Monitor stool frequency and the patient's conscious level and mental state, adjusting the dose to the target number of soft stools daily while watching fluid and electrolyte balance.

Counselling the patient

  • The dose is adjusted to give a set number of soft stools a day, which helps clear the toxins affecting the brain.
  • Carers should report increasing confusion or drowsiness, and seek advice if stools become very loose.

Evidence & guidelines

Lactulose is the established first-line therapy for the treatment and secondary prevention of hepatic encephalopathy in chronic liver disease.

Reference: EASL Guidelines on Hepatic Encephalopathy 2014; NICE Cirrhosis 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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