Lactulose

Lactulose is a synthetic disaccharide of galactose and fructose that is poorly absorbed in the small intestine. It acts as an osmotic laxative and helps lower blood ammonia in hepatic encephalopathy.

Osmosis: The net movement of water across a selectively permeable membrane toward a region with higher solute concentration. Unabsorbed lactulose retains water in the bowel through an osmotic effect.
Constipation: A condition marked by infrequent or difficult passage of stool. Lactulose is prescribed as an osmotic laxative to relieve constipation.
Disaccharide: A carbohydrate composed of two monosaccharide units joined by a glycosidic bond. Lactulose is a disaccharide made from two different sugars.
Diarrhea: The passage of loose or watery stools more frequently than usual. Excessive lactulose dosing can cause diarrhea and fluid loss.
Colonic fermentation: The microbial breakdown of carbohydrates in the colon, producing gases and short-chain fatty acids. Gut bacteria ferment lactulose, acidifying colonic contents and contributing to its laxative action.
Portal-systemic encephalopathy: Brain dysfunction caused by liver disease or blood bypassing the liver, historically termed portal-systemic encephalopathy. This is the clinical setting in which lactulose is used to lower ammonia burden.
Galactose: A six-carbon monosaccharide found in lactose and other biological molecules. One of lactulose’s two sugar units is galactose.
Flatulence: The accumulation or passage of gas from the digestive tract. Colonic fermentation of lactulose commonly produces gas.
Ammonia: A nitrogen-containing compound produced during metabolism and present in biological fluids as NH₃ and NH₄⁺. Lactulose helps reduce intestinal ammonia absorption, relevant to hepatic encephalopathy.
Lactitol: A poorly absorbed synthetic sugar alcohol used as an osmotic laxative and in hepatic encephalopathy. It is a related therapeutic alternative with similar gut-based effects.

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HyperammonemiaRelated: It is commonly used when liver disease contributes to elevated ammonia.