This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Ritonavir inhibits metabolism of all of the following drugs except: 
Select and explain. 
A. Amiodarone, B. Phenytoin, C. Cisapride, D. Midazolam
B: Phenytoin
Answer: B: Phenytoin 
Explanation: Ans. b. Phenytoin (Ref Goodman Gillman Ilth/1302; Katzung II/e plI44)Ritonavir inhibits metabolism of Amiodarone, Cisaprlde, Midazolam and but not the phenytoin'The majority (95%o) of phenytoin is metabolized principalty in the hepatic endoplasmic reticulum by CYP2C9/10 and to a lesser extent CYP2C9.'