What is the mechanism by which lactulose works in the body?

Lactulose is a synthetic disaccharide used primarily in the treatment of constipation and hepatic encephalopathy. Its mechanism of action, particularly in the context of hepatic encephalopathy, involves the conversion of ammonia, a potent neurotoxin, to ammonium. When lactulose is ingested, it is not absorbed in the intestines but instead is fermented by colonic bacteria. This fermentation process results in the production of lactic acid and other short-chain fatty acids, which leads to a decrease in the colonic pH.

As the pH lowers, ammonia (NH3) is converted into ammonium (NH4+), which is positively charged and less likely to cross the intestinal mucosa. This means that ammonium cannot easily enter the bloodstream, thereby reducing the levels of ammonia that can reach the central nervous system, which is beneficial in managing hepatic encephalopathy.

The other options, such as increasing intestinal motility, absorbing excess water, or neutralizing stomach acid, do not accurately represent the principal mechanism by which lactulose exerts its effects. While lactulose does have an osmotic effect that increases water content in the intestines, its primary and most clinically relevant action in the context of liver disease is the conversion