Vardenafil
(Levitra) is an oral drug that is used to treat
impotence (the inability to attain or maintain a penile
erection.). It is a phosphodiesterase inhibitor that is
similar to sildenafil (Viagra).
Penile erection is caused by the engorgement of the
penis with blood. This engorgement occurs when the blood
vessels delivering blood to the penis increase in size
and increase the delivery of blood to the penis. At the
same time, the blood vessels carrying blood away from
the penis decrease in size and decrease the removal of
blood from the penis. Sexual stimulation that leads to
the engorgement and erection causes the production and
release of nitric oxide in the penis. Nitric oxide then
activates the enzyme, guanylate cyclase to produce
cyclic guanosine monophosphate (cGMP). The cGMP is
primarily responsible for increasing and decreasing the
size of the blood vessels carrying blood to and from the
penis, respectively. Vardenafil (Levitra) prevents an
enzyme called phosphodiesterase-5 from destroying cGMP
so that cGMP persists longer. The longer cGMP persists,
the more prolonged the engorgement of the penis.
Vardenafil (Levitra) was approved by the FDA in August,
2003.