Table 1.

Median inhibitory concentration values in nM (fold selectivity versus PDE5).

Compound	PDE1	PDE5	PDE6 (rod)	PDE6 (cone)	Onset (min)	Bio-avilability	Tmax	plasma half life	Route of Clearance	available dose range
Sildenafil	281 (80)	3.5	37 (11)	34 (10)	30–60	∼40%	∼1 h	∼4 h	hepatic	“20–100”
Vardenafil	70 (500)	0.14	3.5 (25)	0.6 (4)	“8–12”	14.50%	∼40 min	∼4 h	hepatic	“5–20”
Tadalafil	>30000 (>4450)	6.74	1260 (187)	1300 (193)	“15–45”	∼36%	∼2 h	15.5 h	hepatic	“5–20”