Erectile dysfunction — vardenafil
The introduction of Viagra (sildenafil) a couple of years ago created a whole new market for pharmaceuticals. Erectile dysfunction was previously a little-discussed condition, but the attention given to Viagra at its launch, and since, has meant many men have been actively seeking drug treatment for the problem.
Sildenafil is an inhibitor of the enzyme phosphodisesterase type 5 (PDE5), which acts on the secondary messenger cyclic guanosine monophosphate (cGMP). The initial aim of the research into PDE5 inhibitors was the treatment of hypertension and angina, and sildenafil was discovered in this area. The subsequent discovery that it also has an effect in erectile dysfunction was serendipitous. PDE5 is present in the corpus cavernosum, and is thought to play an essential role in inducing erection.1
Nitric oxide is released from neurons in the corpus cavernosum, which activates soluble guanyl cyclase, and converts GTP to cGMP. Inhibiting PDE5 stops the conversion of active cGMP to inactive GMP, and cGMP levels build up sufficiently to allow blood to accumulate in the penis and cause erection.
The opening up of the erectile dysfunction market has led to other companies looking to gain a share, and one of these is Bayer, with its developmental drug vardenafil.
A randomised double-blind placebo-controlled trial in 21 patients measured erectile response to visual stimulation. Oral doses of 20 and 40mg both increased by a significant amount the duration of rigidity of the penis. No real difference was found between the effect of the two different doses.2
The drug has been found to be an effective PDE5 inhibitor, and is entering Phase III trials to establish its efficacy and safety.