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Lactulose (Duphalac, Laevolac) belongs to a group of medicines called laxatives. It makes the stool softer and easier to pass, by drawing water into the bowel. It is used in the treatment of constipation and may also be used in the treatment of Chronic portal systemic encephalopathy (hepatic coma): This is an uncommon condition where substances such as ammonia go into the blood stream of patients with severe liver disease.




  • Other brand names: Bifiteral, Bifinorm, Constilac, Constulose, Eugalac, Gatinar, Legendal, Normase, Rudolac, Tulotract




Constipation: When given orally lactulose is poorly absorbed from the gastrointestinal tract and no enzymes capable of hydrolysis of lactulose into its component monosaccharides are known to be present in human gastrointestinal tissue. Lactulose reaches the colon unchanged. There it is metabolised by colonic bacteria to low molecular weight acids ie. lactic acid and other short chain carboxylic acids. The end result is a change in osmotic pressure and acidification of the colonic contents resulting in an increase in stool water-content with resultant distention and softening of the stools, which in turn promotes increased peristalsis and bowel evacuation.

Hepatic encephalopathy: Hepatic encephalopathy is the loss of brain function that occurs when the liver is unable to remove toxins from the blood. Ammonia, which is produced by the body when proteins are digested, is one of the substances normally made harmless by the liver. Lactulose helps trap the ammonia (NH3) in the colon. It does this by using gut flora to acidify the colon, transforming the freely diffusible ammonia into ammonium (NH4+) which can no longer diffuse back into the blood


  • Treatment of constipation. and where a soft stool is considered of medical benefit (haemorrhoids, post colonic/anal surgery).
  • Hepatic encephalopathy, including the stages of hepatic pre-coma and coma.

[edit] DOSAGE

66,7 g/100 ml Oral solution, 3,3 g/5 ml Oral solution, 670 mg/ml :

  • Constipation: Lactulose can take up to 48 hours to have an effect.
  • Adults: Initial: 10-20 g (15-30 mL)/day. Max: 45 mL.
  • Children aged 5 to 10 years: Two x 5ml spoonfuls (10ml), twice a day.
  • Children aged 1 to 5 years: One x 5ml spoonful (5ml), twice a day

  • Portal-Systemic Encephalopathy: The usual dosage is 30 to 45 mL three to four times daily. Maintenance: adjust till patients have regular bowel movements of 2-3 times daily


  • hypersensitivity to the active substance or to any of the excipients
  • galactosaemia (a severe genetic disorder where patient cannot digest galactose)
  • Intestinal obstruction
  • Acute inflammatory bowel disease (like Crohn's disease or ulcerative colitis)


  • Longterm use of unadjusted dosages or misuse can lead to diarrhea and disturbance of the electrolytes balance.


  • Lactulose may increase the loss of potassium induced by other drugs (e.g. thiazides, steroids and amphothericin B).
  • Concomitant use of cardiac glycosides can increase the effect of the glycosides through potassium deficiency.
  • With increasing dosage a decrease of pH-value in the colon is found. Therefore drugs which are released in the colon pH-dependently (e.g. Mesalazine) can be inactivated.


Pregnancy: Lactulose has been shown to be effective for the treatment of constipation associated with pregnancy when administered to women at different stages of pregnancy. Reproduction studies with daily oral doses of lactulose (50% w/w) up to 12 mL per kg in mice and rats and 6 mL per kg in rabbits have not revealed any evidence of an increased occurrence of foetal damage or other deleterious effects.

Lactation: There are no data on the secretion of lactulose in breast milk or the effect on the breast-fed infant. Risk-benefit should be considered.


Diarrhea (dose-related), nausea, vomiting, hypokalaemia, bloating and abdominal cramps.




Drugs for constipation (laxatives and Prokinetic agents)
Softeners, emollients Liquid paraffin
Contact laxatives Bisacodyl (Dulcolax)   Senna   Cascara   Sodium picosulfate
Bulk-forming laxatives Ispaghula
Osmotically acting laxatives Glycerin suppositories   Magnesium salts   Lactulose (Duphalac)   Macrogol   Mannitol   Sorbitol   Sodium phosphate
Prokinetic agents Clebopride   Prucalopride (Resolor)
Others (irritable bowel syndrome accompanied by constipation) Linaclotide (Constella, Linzess)