Lactulose; Uses, Dosage, Side Effects, Drug Interactions

Lactulose; Uses, Dosage, Side Effects, Drug Interactions

Lactulose is a disaccharide (sugar) synthesized from fructose and galactose, Lactulose is used to treat constipation and some liver diseases. Nondigestible in mammals, lactulose passes unabsorbed down to the large intestine where resident bacteria consume it and produce lactic, acetic, and formic acids, which draw fluid into the bowel to soften the stool (laxative effect). Acidification of the colon contents attracts ammonia from the bloodstream, assisting stool excretion; helpful in liver failure when ammonia cannot be detoxified.

Lactulose is a synthetic disaccharide used in the treatment of constipation and hepatic encephalopathy. It has also been used in the diagnosis of gastrointestinal disorders

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 working after eight to twelve hours but may take up to two days to improve constipation.

Mechanism of Action of Lactulose

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.

Indications of Lactulose

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Contra-Indications of Lactulose

Galactose-free diet

Lactulose contains galactose and is contraindicated in patients who require a galactose-free diet.


Lactulose is relatively contraindicated prior to surgery, especially if the procedure requires electrocautery during proctoscopy or colonoscopy. Preoperative use of mannitol can generate a flammable gas (i.e., hydrogen gas), which can explode in the presence of a spark. Although this phenomenon has not been reported with lactulose, caution should be observed.

Diabetes mellitus

Although very little lactulose is absorbed systemically, it should be used with caution in diabetes mellitus patients due to its sugar content (galactose < 1.6 g/15 mL; lactose < 1.2 g/15 mL).

Dosage of Lactulose

Strengths: 10 g/15 mL; 10 g; 20 g

Constipation – Chronic

  • 15 mL orally once a day.

Constipation – Acute

  • Initial dose: 15 mL orally once a day.

Pediatric Dose for Constipation – Chronic

  • Children: 0.7 to 2 g/kg/day (1 to 3 mL/kg/day) orally in divided doses daily; generally recommended not to exceed the adult maximum of 40 g/day (60 mL/day).

Side Effects of Lactulose

The most common

More common

  • Black, tarry stools
  • bleeding gums
  • bloating or swelling of the face, arms, hands, lower legs, or feet
  • blood in the urine or stools
  • confusion
  • cough or hoarseness
  • crying
  • dementia
  • depersonalization
  • diarrhea
  • difficult or labored breathing
  • dysphoria
  • euphoria
  • fever or chills
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Less common

  • Abdominal or stomach discomfort
  • black, tarry stools
  • blood in the stools
  • chest discomfort or pain
  • chills
  • cold or flu-like symptoms
  • cough
  • difficult or labored breathing
  • fever
  • general feeling of discomfort or illness
  • headache
  • increased sweating
  • joint pain
  • loss of appetite
  • loss of bowel control
  • muscle aches and pains
  • runny nose
  • shivering
  • sore throat
  • sweating
  • tightness in the chest

Drug Interactions of Lactulose

There have been conflicting reports about the concomitant use of neomycin and lactulose solution. Theoretically, the elimination of certain colonic bacteria by neomycin and possibly other anti-infectiveagents may interfere with the desired degradation of lactulose and thus prevent the acidification of colonic contents. Thus the status of the lactulose-treated patient should be closely monitored in the event of concomitant oral anti-infective therapy.

Results of preliminary studies in humans and rats suggest that nonabsorbable antacids given concurrently with lactulose may inhibit the desired lactulose-induced drop in colonic pH. Therefore, a possible lack of the desired effect of treatment should be taken into consideration before such drugs are given concomitantly with lactulose.

Other laxatives should not be used, especially during the initial phase of therapy for portal-systemic encephalopathy because the loose stools resulting from their use may falsely suggest that adequate lactulose dosage has been achieved.

Pregnancy & Lactation of Lactulose

FDA Pregnancy Category B


This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.


It is not known if this medication passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

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