Cephulac, Chronulac, Cholac, Constulose, Enulose, Kristalose


  • Solution/Syrup: 10 g lactulose per 15 mL or 30 mL (also comes in larger volumes)
  • Crystals for reconstitution: 10 g and 20 g


Lactulose belongs to the class of ammonia detoxicants. A synthetic derivative of lactose, lactulose is a non-digestible disaccharide formed from fructose and galactose. It acts as an osmotic laxative and as an acidifier of contents in the colon.

Lactulose is poorly absorbed following oral administration, reaching the colon unchanged where it exerts its effect. A small portion, approximately 0.4-2% that is absorbed from the small intestine, is excreted unchanged in urine. As the digestive bolus moves through the intestine, residential bacteria in the colon metabolizes and degrades lactulose into lactic acid and acetic acid, acidifying intestinal contents and promoting retention of water content in feces through osmosis, making the feces softer and easier to pass. This makes lactulose effective as a laxative. In addition, the acids produced by the degradation of lactulose causes ammonia to move from the blood into the colon where it is trapped in the form of ammonium ion and eliminated in feces allowing lactulose to be used in the treatment of PSE (portal-systemic [hepatic] encephalopathy) to reduce ammonia blood levels.

In studies of mice, rats, and rabbits, doses of lactulose solution up to 6 or 12 mL/kg/day produced no deleterious effects in breeding, conception, or parturition.

Lactulose is not thought to be excreted in breast milk.


Used as a stool softener in conditions such as megacolon, or in the treatment of hepatic encephalopathy to reduce ammonia blood levels.

Drug Interactions or Contraindications

  • Combining with antacids may reduce colonic acidification and efficacy of lactulose.
  • It is thought that antibiotics, in particular neomycin, could theoretically eliminate residential colonic bacteria responsible for metabolizing lactulose, reducing the efficacy of lactulose. However, there is also suggestion that combined use may be beneficial when treating portal-systemic (hepatic) encephalopathy.
  • The stool softening effects of lactulose can be compounded by the use of additional laxatives; therefore, it is advised not to use together.

Adverse Reactions

GI: Intestinal cramping, gas (flatus), dehydration, diarrhea (which can be avoided by reducing amount of lactulose)

Dosage Recommendations

0.5 mL/kg, PO, q12hr  34, 35, 41, 42, 44


  • Lactulose is sweet tasting and may be accepted well by rats.
  • Lactulose should not be taken by diabetics. Although lactulose is not readily absorbed by the intestine, there is a small percentage which is. In addition, lactulose syrup contains some unbound fructose and galactose, which may pose a problem in animals with diabetes.
  • Avoid using in rats with preexisting dehydration as doing so can result in electrolyte imbalances.
  • Store lactulose at room temperature away from light. Exposure to heat and light can cause cloudiness and darkening of the solution but is not believed to affect potency.
  1. Evered, D., & Sadoogh-Abasian, F. (1979). Absorption of lactulose from mammalian gastrointestinal tract. British Journal of Nutrition, 41(1), 47-51.
  2. Lactulose. (2005, August 1). Retrieved January 26, 2015, from


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