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': 'Among the following, which of the following 5-PDE inhibitor has the longest duration of action? \nSelect and explain. \nA. Sildenafil, B. Vardenafil, C. Tadalafil, D. Udenafil', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Tadalafil o Tadalafil is the longest acting phosphodiesterase inhibitor used for erectile dysfunction. Its half life is 17.5 hours.", 'role': 'assistant'}]