Lactulose is used in cirrhosis to detoxify ammonium and act as an osmotic laxative. Which statement best describes its action?

• A. Decreases intestinal bacteria.
• B. Acts as a bile acid sequestrant.
• C. Detoxifies ammonium and acts as an osmotic laxative.
• D. Increases potassium absorption.

Answer: (C)

Lactulose works in cirrhosis by lowering colonic pH and drawing water into the intestine, a combination that reduces ammonia reaching the brain. In the colon, gut bacteria ferment lactulose to short-chain acids, lowering the luminal pH. The more acidic environment converts ammonia (NH3) to ammonium (NH4+), which is trapped in the gut and excreted rather than absorbed into the bloodstream. At the same time, lactulose acts as an osmotic laxative, pulling water into the colon and increasing stool water content, which speeds stool passage and enhances elimination of the ammonia-cycle waste products. This dual action—detoxifying ammonium and serving as an osmotic laxative—best describes how lactulose helps in hepatic encephalopathy.

It isn’t primarily about decreasing intestinal bacteria, and it isn’t a bile acid sequestrant, nor does it mainly function by increasing potassium absorption.