Neomycin is used in hepatic encephalopathy to reduce ammonia by what mechanism?

• A. Inhibits bacterial protein synthesis in the gut
• B. Kills bacteria in the gut that generate ammonia
• C. Inhibits hepatic urea cycle enzymes
• D. Scavenges ammonia in the bloodstream

Answer: (B)

Hepatic encephalopathy is driven by ammonia produced by gut bacteria. Neomycin acts as a nonabsorbable antibiotic that stays in the gut and reduces the population of bacteria that generate ammonia, leading to lower intestinal ammonia production. While its general action is to inhibit bacterial protein synthesis, the clinically relevant effect here is decreasing the number of ammonia-producing bacteria in the gut. That’s why the mechanism by which it reduces ammonia is killing bacteria in the gut that generate ammonia.