Lactulose

Lactulose is an osmotic laxative and a synthetic disaccharide. It cannot be digested by human digestive enzymes and passes almost intact through the small intestine into the colon. In the colon, it is metabolized by gut bacteria into short-chain organic acids such as lactic acid and acetic acid, lowering the luminal pH. The acidic environment and the unabsorbed lactulose molecules increase osmotic pressure within the intestinal lumen, drawing water into the bowel, softening stool, increasing stool volume, stimulating intestinal motility, and facilitating defecation. In hepatic encephalopathy, acidification of the colon converts absorbable ammonia (NH₃) into less absorbable ammonium ions (NH₄⁺), thereby reducing ammonia entry into the bloodstream.