This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy: General Principles, Subject name: Pharmacology
All of the following cause inhibition of CYP3A except. 
Select and explain. 
A. Saquinavir, B. Ritonavir, C. Itraconazole, D. Erythromycin
A: Saquinavir
Answer: A: Saquinavir 
Explanation: Ans. (A) Saquinavir(Ref: Katzung 11th/e p58, 863)All the drugs given in the options are microsomal enzyme inhibitors. Among protease inhibitors, ritonavir is the strongest inhibitor of CYP3A4 enzymes whereas saquinavir is the weakest.