Which medication decreases ammonia levels in hepatic encephalopathy?

• A. Rifaximin
• B. Neomycin
• C. Metronidazole
• D. Lactulose

Answer: (D)

Managing hepatic encephalopathy centers on lowering ammonia entering the brain. Lactulose is the best choice because it works in the gut to reduce ammonia absorption and production. It is not absorbed and is fermented by colonic bacteria into acids that lower the colonic pH. This acidic environment converts ammonia (NH3) to ammonium (NH4+), which is not easily absorbed, and the laxative effect speeds stool passage, further reducing the time ammonia can be produced and absorbed. The result is a notable drop in serum ammonia and improvement in mental status.

The other medications—rifaximin, neomycin, and metronidazole—kill or suppress gut bacteria that generate ammonia, so they’re useful as adjuncts or alternatives, but they don’t lower ammonia as directly or quickly as lactulose does when used as first-line therapy. Monitor for lactulose-related effects like diarrhea and electrolyte shifts.