Lactulose: Indication, dosage and side effects

Lactulose: Indication, dosage and side effects

Lactulose: Indication, dosage and side effects

Lactulose is a non-absorbable sugar used in the treatment of constipation and hepatic encephalopathy. It is used by mouth for constipation and either by mouth or in the rectum for hepatic encephalopathy. It generally begins work ing after 8-12 hours, but may take up to 2 days to improve constipation. This drug is used by mouth or rectally to treat or prevent complications of liver disease (hepatic encephalopathy). It does not cure the problem, but may help to improve mental status. Lactulose is a colonic acidifier that works by decreasing the amount of ammonia in the blood. It is a man-made sugar solution.



Lactulose is used in the treatment of chronic constipation in patients of all ages as a long-term treatment. The dosage of lactulose for chronic idiopathic constipation is adjusted depending on the constipation severity and desired effect, from a mild stool softener to causing diarrhea. Dosage is reduced in case of galactosemia, as most preparations contain the monosaccharide galactose due to its synthesis process.


Lactulose is useful in treating high blood ammonia, which can lead to hepatic encephalopathy. Lactulose helps trap the ammonia (NH3) in the colon and bind to it. It does this by using gut flora to acidify the colon, transforming the freely diffusible ammonia into ammonium ions (NH+4), which can no longer diffuse back into the blood. It is also useful for preventing hyperammonemia caused as a side effect of administration of valproic acid.

Small intestine bacterial overgrowth

Lactulose is used as a test of small intestine bacterial overgrowth (SIBO). Recently, the reliability of it for diagnosing SIBO has been seriously questioned. A large amount of it is given with subsequent testing of molecular hydrogen gas in the breath. The test is positive if an increase in exhaled hydrogen occurs before that which would be expected by normal colonocyte digestion. An earlier result has been hypothesized to indicate digestion occurring within the small intestine. An alternate explanation for differences in results is the variance in small bowel transit time among tested subjects.

Side effects

· dehydration · diarrhea · excessive bowel activity · high blood sodium levels · low blood sodium levels · nausea · vomiting · abdominal cramping · abdominal distention · burping (belching) · gas (flatulence)


 20-30 g (30-40 ml) orally every hour to induce rapid defecation; reduced to 20-30 g every 6-8 hours after defecation achieved; titrated to produce 2-3 soft stools/day


300 ml (200 g) rectally with 700 ml water or normal saline, retained for 30-60 minutes; may be repeated every 4-6 hours; transition to oral treatment before discontinuance of rectal administration  

Infants: 2.5-10 ml/day (1.7-6.67 g/day) orally in divided doses; titrated to produce 2-3 soft stools per day

Children and adolescents: 40-90 ml/day (26.7-60 g/day) orally in divided doses; titrated to produce 2-3 soft stools/day


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