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
Which of the following agent is not used in erectile dysfunction: 
Select and explain. 
A. PGE2, B. Vardenafil, C. Phenylephrine, D. Alprostadil
C: Phenylephrine
Answer: C: Phenylephrine 
Explanation: Alpha blockers are used in erectile dysfunction not alpha agonists (phenyephrine).
Drugs useful in the management of erectile dysfuncLion (ED)
1. Phosphodiesterase inhibitors

Sildenafil
Vardenafi
Tadalafil
Udenafil

2. PGE1 analog - Alprostadil
3. Aviptadil