What It Does: Sildenafil (Viagra) is a phosphodiesterase inhibitor. It is administered orally for the treatment of male erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).

Brief History of Viagra: Sildenafil was originally developed as an antianginal agent but was found to be more effective in treating ED and subsequently PAH. In regards to ED, sildenafil (Viagra®) was the first drug with this mechanism of action to be marketed; it is not a prostaglandin inhibitor. As opposed to other therapies for impotence which require direct injection into the penis or insertion of a urethral suppository, sildenafil is given orally. The drug was tested in more than 4000 men in 21 clinical trials. The average age of these men was 55 years and they had erectile dysfunction for an average of 5 years before entering the study. Sildenafil was effective in roughly 70% of subjects. Response rates of 90% have been achieved in trials of male patients with psychogenic impotence. Sildenafil may also be effective in male patients with impotence related to diabetes mellitus or due to pelvic fracture urethral disruption. In a study comparing oral sildenafil to sublingual apomorphine, an investigational ED drug, sildenafil was significantly more effective than apomorphine. Sildenafil has been shown to be effective and well tolerated in patients on multidrug antihypertensive regimens and not associated with additional safety risks in these patients.
Final FDA approval for sildenafil (Viagra®) for the treatment of erectile dysfunction (ED) in men was granted on March 27, 1998.

Not Just for Erectile Dysfunction: Sildenafil continues to be studied clinically to assess its utility in treating sexual dysfunction in females, but initial studies have found sildenafil to provide results similar to placebo in women. Shortly after approval for ED, studies showed sildenafil was effective in treating patients with PAH. Sildenafil improved exercise capacity as well as mean pulmonary artery pressure and other measures of cardiac function in patients with PAH. Sildenafil is the first oral therapy approved for treating early stages of PAH. Sildenafil has also shown efficacy in treating altitude sickness. Due to a risk of cardiovascular adverse events, this drug should not be used in patients taking nitrate therapy such as GTN.

Final FDA approval for sildenafil (Revatio™) for treatment of pulmonary arterial hypertension (PAH) was granted June 3, 2005.