Pharmacology: Pharmacodynamics: Lactulose is a synthetic disaccharide osmotic laxative used in the treatment of constipation and in hepatic encephalopathy. Lactulose is broken down by colonic bacteria mainly into lactic acid. This exerts a local osmotic effect in the colon resulting in increased faecal bulk and stimulation of peristalsis. It may take up to 48 hours before an effect is obtained. When larger doses are given for hepatic encephalopathy, the pH in the colon is reduced significantly and the absorption of ammonium ions ad other toxic nitrogenous compounds is decreased, leading to a fall in blood-ammonia concentration and an improvement in mental function.
Pharmacokinetics: Taken orally, lactulose passes essentially unchanged into the large intestine where it is metabolized by saccharolytic bacteria with the formation of simple organic acids, mainly lactic acid and small amounts of acetic and formic acids. The small amount of absorbed lactulose is subsequently excreted unchanged in the urine.