ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Osmotic Laxative / Ammonia-Reducing Agent Pregnancy: Compatible — not systemically absorbed

Lactulose (Hepatic Encephalopathy)

Brand names: Duphalac

Adult dose

Dose: Hepatic encephalopathy: 30–50 mL TDS–QDS (adjust to produce 2–3 soft stools/day). Constipation: 15 mL BD.
Route: Oral or via NG tube/rectal enema
Frequency: TDS–QDS for encephalopathy
Max: 200 mL/day (encephalopathy)
For hepatic encephalopathy: target 2–3 soft stools per day to reduce gut transit time and ammonia production. Can be given as rectal enema (300 mL in 700 mL water) for acute HE.

Paediatric dose

Route: Oral
Frequency: BD-TDS
Max: Constipation: infants <1 yr: 2.5 mL BD; 1–5 yr: 5 mL BD; 5–10 yr: 10 mL BD; >10 yr: 15 mL BD
Concentration: 3.35 g/5 mL (667 mg/mL) mL/ml
Hepatic encephalopathy in children: adjust dose to produce 2–3 soft stools per day under specialist supervision

Dose adjustments

Renal

No dose adjustment required

Hepatic

Use with care — primary use is for hepatic complications; adjust to bowel habit

Clinical pearls

  • Mechanism in HE: acidifies colon (ammonium ion formation), alters gut flora, reduces ammonia-producing bacteria, increases gut transit
  • NICE: rifaximin 550 mg BD added to lactulose as second-line for prevention of recurrent HE episodes
  • Lactulose enema preferred route in acute HE with impaired swallowing/consciousness
  • Overtreating can cause severe diarrhoea and electrolyte imbalance — aim for 2–3 soft stools/day, not watery diarrhoea

Contraindications

  • Galactosaemia
  • Intestinal obstruction
  • Galactose or lactose intolerance

Side effects

  • Flatulence and bloating (very common)
  • Diarrhoea (overdose)
  • Nausea
  • Electrolyte disturbance with prolonged high doses
  • Abdominal cramps

Interactions

  • Antacids — may alter colonic pH and reduce efficacy slightly
  • Mesalazine — acidic colon pH may reduce mesalazine release from pH-dependent formulations

Monitoring

  • Stool frequency and consistency
  • Electrolytes (sodium, potassium) with high doses
  • Level of consciousness in HE (West Haven criteria)
  • Serum ammonia (trend)
  • Fluid balance

Reference: BNFc; BNF; EASL Guidelines on Hepatic Encephalopathy 2014; NICE Cirrhosis Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways