Lactulose reduces arterial ammonia in hepatic encephalopathy primarily through which mechanism?
- A Binding ammonia directly in the portal circulation before it reaches the systemic circulation
- B Increasing urea synthesis in periportal hepatocytes through glutamine synthetase induction
- C Acidifying colonic contents so ammonia is trapped as non-absorbable ammonium ion ✓
- D Promoting renal excretion of ammonia via glutamine release in proximal tubules
Correct answer: C. Acidifying colonic contents so ammonia is trapped as non-absorbable ammonium ion
Explanation
Lactulose is a non-absorbable disaccharide fermented by colonic bacteria to lactic and acetic acids. The resulting acidic luminal pH converts absorbable ammonia into ammonium ions that cannot cross the gut wall, trapping nitrogen in stool; its cathartic action then expels this load. It does not bind ammonia chemically, and rifaximin acts separately by reducing ammoniagenic gut flora.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.