Lactulose Uses

Lactulose is used to treat chronic constipation. It is also used to reduce the amount of ammonia in the blood of people with hepatic encephalopathy. This is a reversible complication of liver dysfunction in which there are mental status changes due to the accumulation of certain toxic substances in the body.

There may be other uses of lactulose—your doctor or health system pharmacists can give you further drug information.

Lactulose Mechanism of Action

Lactulose relieves constipation by drawing water into the colon (large intestine) and making the stool softer and easier to pass. In people with hepatic encephalopathy, lactulose pulls ammonia into the colon, from where it is eliminated from the body.  

Lactulose Doses

Lactulose comes as a 10 g and 20 g packet of crystals and a 10 g/15 mL oral/rectal solution. 

The usual dose of lactulose in adults is as follows:

• For the treatment of constipation: Lactulose is usually prescribed at a dose of 15-30 mL (10-20 grams) by mouth once daily. This dose can be increased to 60 mL (40 grams) once daily, if needed. The crystals should be taken at a dose of 10-20 grams by mouth once daily, with a maximum dose of 40 grams/day.
• For the prevention of hepatic encephalopathy: The dose is usually 30-45 mL (20-30 grams) by mouth every 6-8 hours. This dose is adjusted until 2-3 soft stools occur per day. The dose can be given more frequently, every 1-2 hours, if needed, to produce 2-3 soft stools a day.
• For the treatment of hepatic encephalopathy: The dose is 30-45 mL (20-30 grams) by mouth every hour to induce rapid bowel movements. This dose may be reduced to 20-30 grams every 6-8 hours after you have a bowel movement. The dose will be adjusted to produce 2-3 soft stools a day. 
• For rectal administration: Lactulose 300 mL (200 grams) is mixed with 700 mL of water or normal saline and instilled into the rectum. The solution is retained for 30-60 minutes. The treatment can be repeated every 4-6 hours. A transition to oral lactulose should be made before discontinuing rectal administration.