What Factors Affect Lactulose Dosage?

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  • Written By: Canaan Downs
  • Edited By: Kaci Lane Hindman
  • Last Modified Date: 09 August 2019
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Despite its reputation as a potent, if unconventional, treatment for stubborn cases of constipation, lactulose is regarded as a remarkably safe medication. While this carbohydrate molecule cannot be digested or absorbed by the human body, natural intestinal flora are able to consume the sugar, producing various biologically active waste products as a result. These bacterial waste products include stool-bulking agents like intestinal gas, peristalsis-promoting acids, and indirect stool-softening chemicals like carboxylic acids, all of which serve to facilitate the evacuation of the bowels. The increased intestinal acidity produced by the bacterial metabolism of lactulose also serves to favor the production of ammonium over ammonia in the gut, suggesting that a higher lactulose dosage may help prevent or treat hepatic or portal-systemic encephalopathy. When used to treat either encephalopathy or constipation in pediatric patients a lower lactulose dosage may be employed.


The drug is typically administered as a liquid, either orally or rectally in the form of an enema. Adults receiving treatment for chronic constipation typically receive an initial lactulose dosage of 15 mL orally once per day. While a second maintenance dose may be recommended at bedtime, the tendency of the medication to promote the urgent need to evacuate the bowels makes this inadvisable. Many physicians instead prefer to re-evaluate the starting lactulose dosage, increasing the dose in small increments as required to achieve a symptomatic breakthrough before then decreasing the dose to a level sufficient to control symptoms. Increases in dose, however, are often accompanied by the increased incidence and severity of side-effects such as flatulence, intestinal bloating and cramps.

While the same lactulose dosage guidelines may be followed to treat adults with acute constipation, children with either acute or chronic diarrhea should receive a lower dose. The recommended initial dose for pediatric patients is between 1 and 3 mL per 2.2 lbs (about 1 kg) of body weight given in divided doses throughout the day. No more than 60 mL of the drug should be used by either children or adults within a 24-hour period, as the symptoms of overdose can be potentially life-threatening.

The treatment of portal-systemic or hepatic encephalopathy in adults is three daily oral doses of 30 mL, much higher than that recommended initially for the treatment of constipation. A maintenance dose of 30 to 45 mL may be given three times per day as well. In severe cases, 30 to 45 mL of lactulose may be administered hourly until symptoms resolve. Children under the age of 14 generally receive 40 mL to 90 mL of the drug per day in divided doses, while infants should be given 2.5 to 10 mL in the same manner. If diarrhea is produced, patients should cease treatment until normal bowel function is achieved, then evaluate the effects of a lower dosage level.


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