The erectile disorder in males is more specifically treated with which of the following agents?

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