This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
[{'content': 'Which of the following laxatives lowers blood ammonia level in hepatic encephalopathy? \nSelect and explain. \nA. Bisacodyl, B. Liquid paraffin, C. Lactulose, D. Magnesium sulfate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: (Ref: KDT 6/e p655) Lactulose is degraded to lactic acid that conves NH3 to NH4+. As ionic molecules cannot cross biological membranes, it is not absorbed and is thus excreted.', 'role': 'assistant'}]