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
Among the following, which of the following 5-PDE inhibitor has the longest duration of action? 
Select and explain. 
A. Sildenafil, B. Vardenafil, C. Tadalafil, D. Udenafil
C: Tadalafil
Answer: C: Tadalafil 
Explanation: 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.