ATCvet code: QA06AD11

Lactulose is a disaccharide (galactose/fructose) that is not hydrolysable by mammalian gut enzymes. Upon reaching the colon, lactulose is metabolized by the resident bacteria resulting in the formation of low molecular weight acids (lactic, formic and acetic acid) and CO2. These acids have a dual effect; they increase osmotic pressure drawing water into the bowel causing a laxative effect and also acidify colonic contents. The acidification causes NH3 (ammonia) to migrate from the blood into the colon where it is trapped as [NH4]+ (ammonium ion) and expelled with the faeces.

Lactulose is poorly absorbed after oral administration and it reaches the colon unchanged. In dogs and cats, less than 2% of an oral dose of lactulose is absorbed (in the small intestine). The absorbed drug is not metabolized and excreted unchanged in the urine within 24 hours.