Erectile dysfunction - udenafil

The advent of Viagra (sildenafil) generated a new "disease" of erectile dysfunction (ED). Its discovery had been serendipitous, and other companies soon moved into the market, with other phosphodiesterase type 5 inhibitor drugs, namely Cialis (tadalafil) and Levitra (vardenafil), being introduced by Lilly and Bayer.

Despite the already crowded market, further drugs in the class are being developed. One of these, udenafil, is being investigated by Korean company Dong-A. It has a similar activity profile to sildenafil but lacks the PDE11 activity of tadalafil, which may be associated with myalgia and testicular toxicity. It has a relatively long half life of 11 to 13 hours and fast absorption, which would give it both a fast onset of action and long duration.

In a double blind placebo-controlled Phase I study, 42 healthy male volunteers were given doses ranging from 12.5 to 300mg of the drug or placebo.¹ It was well tolerated, and the mean terminal half life was between seven and 12 hours. The incidence of adverse events increased with dose. A second Phase I study looked at single doses of 50, 100, 200 and 400mg, and multiple doses of 100 and 200mg/day for 10 days.² Again, it was well tolerated, and multiple dosing did not lead to accumulation of the drug in the body.

A multicentre randomised double blind placebo-controlled parallel group Phase II study was carried out in 319 patients with ED. Those given 100 and 200mg doses had significantly higher erectile function scores after 12 weeks than those given placebo, and 40% of those given the higher dose returned to normal function after the 12 weeks compared with just 9% of the placebo group. It was well tolerated with low incidence of minor side-effects, and no cases of myalgia were seen.