The present invention generally relates to the transdermal delivery of sildenafil and other phosphodiesterase type 5 inhibitors. While transdermal transport of sildenafil in creams and other topical formulations have been previously described, propylene glycol has not previously been recognized as a transdermal enhancer. However, in some aspects of the present invention, certain concentrations of propylene glycol can have a surprising effect on the transdermal delivery of sildenafil and other phosphodiesterase type 5 inhibitors, e.g., doubling the amount of transdermal delivery in some cases.
