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
[{'content': 'Mechanism of action of sildenafil is: March 2012 \nSelect and explain. \nA. 5 alpha reductase inhibitor, B. Antiandrogen, C. Phosphodiesterase-5 inhibitor, D. Androgenic', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans: C i.e. Phosphodiesterase-5 inhibitor Drugs and mechanism of action Finsateride is a competitive inhibitor of the enzyme 5 alpha reductase (which conves testosterone into more active dihydrotestosterone) Flutamide is a non-steroidal drug having specific anti-androgenic, but no other hormonal activity Sildenafil acts by selectively inhibiting PDE-5 and enhancing nitric oxide action in corpus cavernosum Danazol is an orally active ethisterone derivative having weak androgenic, anabolic and progestational activities.', 'role': 'assistant'}]