lactulose (Constulose, Enulose, Generlac, Cholac, Constilac)

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

GENERIC NAME: lactulose laxative

BRAND NAME: Constulose, Enulose, Generlac, Cholac, Constilac

DISCONTINUED BRAND(S): Acilac, Cephulac, Chronulac, Portalac, Evalose, Laxilose, Duphalac, Heptalac

DRUG CLASS AND MECHANISM: Lactulose is a man-made sugar that contains two naturally occurring sugars, galactose and fructose. It is not digested in the intestine like other sugars so that it reaches the colon where bacteria digest it and thereby alter the composition of the stool.

Lactulose is used as a laxative to treat constipation. In the colon, lactulose is broken down by bacteria into products that help to draw water into the colon, which softens the stool.

Additionally, lactulose is used to treat hepatic encephalopathy, a loss of brain function and change in mentation that occurs when the liver is unable to remove toxins from the blood. Bacteria in the colon digest lactulose into chemicals that bind ammonia that is believed to be the toxin that causes hepatic encephalopathy. The binding of ammonia prevents ammonia from moving from the colon into the blood and also draws ammonia from the blood and into the colon. The bound ammonia then is removed from the body in the stool.

The FDA approved lactulose in March, 1976.

PRESCRIBED FOR: Lactulose is used to treat constipation and to prevent and treat hepatic encephalopathy.

SIDE EFFECTS: Common side effects include

Diarrhea may occur if the dose is too high. Serious complications associated with diarrhea are fluid loss (dehydration), high amounts of sodium in the blood (hypernatremia), and low amounts of potassium in the blood (hypokalemia).


Diarrhea (loose stool) may occur if the dose of lactulose is too high. Problems associated with diarrhea are fluid and potassium loss in the diarrheal stool leading to dehydration and low blood levels of potassium (hypokalemia). An additional side effect is the elevation of blood levels of sodium (hypernatremia) as a result of the loss of fluid.

Lactulose contains sugars (galactose and lactose) and should be used cautiously in people with diabetes; however, since lactulose is not digested, and little of the sugar is absorbed, the effects in people with diabetes usually are minimal.

Medically Reviewed by a Doctor on 9/22/2015

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