Sildenafil citrate (Viagra).

Sildenafil citrate, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type V (PDE V), initially designated as compound 92-480-10 by Pfizer, was studied in the late 1980s as an antianginal. An unexpected side effect of the early clinical investigations was improved erectile function among the men studied. This serendipitous finding has transformed the field of erectile dysfunction therapy (1-3). The novelty of this compound is its oral route of delivery and efficacy across a broad range of etiologies.