This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
The erectile disorder in males is more specifically treated with which of the following agents? 
Select and explain. 
A. Sildenafil, B. Diazepam, C. Fluoxetine, D. Zolpidem
A: Sildenafil
Answer: A: Sildenafil 
Explanation: Sldenafil: Sildenafil acts by selectively inhibiting PDE-5 and enhancing NO action in corpus cavernosum. Penile tumescence during sexual arousal is improved, but it has no effect on penile tumescence in the absence of sexual activity. It does not cause priapism in most recipients. Oral bioavailability of sildenafil is -40%, peak blood levels are attained in 1-2 hr; also used for pulmonary HTN Side effects are mainly due to PDE-5 inhibition related vasodilatation- headache, nasal congestion, dizziness, flushing and fall in BP, loose motions. Sildenafil, in addition, weakly inhibits the isoenzyme PDE-6 which is involved in photoreceptor transduction in the retina. As such, impairment of colour vision, especially blue-green discrimination, occurs in some recipients. ESSENTIAL of medical PHARMACOLOGY SIXTH EDITION -KD TRIPATHI Page:295