Oral phentolamine: an alpha-1, alpha-2 adrenergic antagonist for the treatment of erectile dysfunction

Phentolamine mesylate is an alpha-1 and alpha-2 selective Adrenergic Receptor antagonist which has undergone clinical trials for erectile dysfunction treatment. Biochemical and physiological studies in human erectile tissue have revealed a high affinity of phentolamine for alpha-1 and alpha-2 adrenergic receptors. Based on pharmacokinetic studies, it is suggested that 30-40 min following oral ingestion of 40 or 80 mg of phentolamine (Vasomax), the mean plasma phentolamine concentrations are sufficient to occupy the alpha-1 and -2 adrenergic receptors in erectile tissue and thereby result in inhibition of adrenergic-mediated physiologic activity. In large multi-center, placebo-controlled pivotal phase III clinical trials, the mean change in the erectile function domain of the International Index of Erectile Function scores (Questions 1-5 and 15) from screening to the end of treatment was significantly higher following use of active drug (40 mg and 80 mg) compared to placebo. Three to four times as many patients receiving phentolamine reported being satisfied or very satisfied compared with those receiving placebo. At doses of 40 mg and 80 mg respectively, 55% and 59% of men were able to achieve vaginal penetration with 51% and 53% achieving penetration on 75% of attempts. The correction of erectile dysfunction or improvement to a less severe category of dysfunction was experienced by 53% of men with the 80 mg dose and 40% with the 40 mg dose of phentolamine. All trends of response were the same regardless of any concomitant medication. There were no severe adverse events. At 40 mg, 7.7% experienced rhinitis and fewer than 3.1% experienced any other side effect of treatment. Phentolamine is safe, well tolerated and efficacious for the treatment of erectile dysfunction.