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2D structure from PubChem
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Generic Names
Trade Names
  • Acilac
  • Bifiteral
  • Cephulac
  • Cholac
  • Chronulac
  • Constilac
  • Constulose
  • D-Lactulose
  • Duphalac
  • Enulose
  • Evalose
  • Fructofuranose
  • Generlac
  • Heptalac
  • Isolactose
  • Kristalose
  • Lactulosa [INN-Spanish]
  • Lactulosa [Spanish]
  • Lactulose [USAN:BAN:INN:JAN]
  • Lactulose, ~98%
  • Lactulosum [INN-Latin]
  • Lactulosum [Latin]
  • Laevolac
  • Lattulosio [Italian]
  • Laxilose
  • Portalac
Brand Mixture Names

PharmGKB Accession Id:


A synthetic disaccharide used in the treatment of constipation and hepatic encephalopathy. It has also been used in the diagnosis of gastrointestinal disorders. (From Martindale, The Extra Pharmacopoeia, 30th ed, p887)

Source: Drug Bank


For the treatment of constipation and hepatic encephalopathy.

Source: Drug Bank

Other Vocabularies

Information pulled from DrugBank has not been reviewed by PharmGKB.

Pharmacology, Interactions, and Contraindications

Mechanism of Action

Lactulose is a synthetic sugar used in the treatment of constipation and liver disease. It consists of the monosaccharides fructose and galactose. In the colon, lactulose is broken down primarily to lactic acid, and also to small amounts of formic and acetic acids, by the action of via evolved-beta galactosidase from colonic bacteria, which results in an increase in osmotic pressure and slight acidification of the colonic contents. This in turn causes an increase in stool water content and softens the stool. In treating heptic diseases (hepatic encephalopathy) it is thought that lactulose draws out ammonia from the body in the same way that it draws out water into the colon.

Source: Drug Bank


Therapeutically, lactulose has laxative and ammonia-detoxifying actions. In treating constipation lactulose metabolites draw water into the bowel, causing a cathartic effect through osmotic action.

Source: Drug Bank

Food Interaction

Take without regard to meals. Drink liberally.

Source: Drug Bank

Absorption, Distribution, Metabolism, Elimination & Toxicity


Lactulose is completely metabolized in the colon by enteric bacteria, and no lactulose is excreted in the feces.

Source: Drug Bank


Poorly absorbed from the gastrointestinal tract as no human enzyme that is capable of hydrolysis of this disaccharide is present in human gastrointestinal tissue.

Source: Drug Bank


1.7-2 hours

Source: Drug Bank


LD 50=18.2 g/kg (oral, rat). Side effects include diarrhea and resultant dehydration.

Source: Drug Bank

Route of Elimination

The primary route of elimination is fecal. Urinary excretion has been determined to be 3% or less and is essentially complete within 24 hours.

Source: Drug Bank

Chemical Properties

Chemical Formula


Source: Drug Bank

Isomeric SMILES


Source: Drug Bank


Source: Drug Bank

Canonical SMILES


Source: Drug Bank

Average Molecular Weight


Source: Drug Bank

Monoisotopic Molecular Weight


Source: Drug Bank

Publications related to lactulose: 1

No Dosing Guideline available No Drug Label available No Clinical Annotation available No Variant Annotation available No VIP available No VIP available
Prediction of adverse drug reactions using decision tree modeling. Clinical pharmacology and therapeutics. 2010. Hammann F, et al. PubMed


Web Resource:
National Drug Code Directory:
KEGG Compound:
KEGG Drug:
PubChem Compound:
PubChem Substance:
Drugs Product Database (DPD):
FDA Drug Label at DailyMed:

Clinical Trials

These are trials that mention lactulose and are related to either pharmacogenetics or pharmacogenomics.

No trials found.

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Sources for PharmGKB drug information: DrugBank, Open Eye Scientific Software.