General Information: Levitra, belongs to the phosphodiesterase type 5 (PDE5) inhibitors drug class, a class of drugs commonly indicated for treatment of erectile dysfunction (ED). It is a selective phosphodiesterase (PDE) type 5 inhibitor similar to sildenafil and tadalafil. This class of drugs does not inhibit prostaglandins as do some agents for treating ED (e.g., alprostadil). Levitra and tadalafil are more selective for PDE5 than PDE6, which is present in the retina. This leads to less visual adverse effects such as those reported in sildenafil-treated patients. The advantage of Levitra may be that it achieves maximum plasma concentration sooner than sildenafil and tadalafil which may result in a faster onset of action. In an analysis of 580 patients, erections improved in 80% of men, and the ability to complete sexual intercourse with ejaculation was increased. Efficacy in treating diabetics and radical prostectomy patients has also been demonstrated. According to ED treatment guidelines, oral phosphodiesterase type 5 inhibitors (PDE5 inhibitor) are considered first-line therapy. Levitra was approved by the FDA in August 2003 for erectile dysfunction. An orally disintegrating tablet was approved by the FDA in June 2010.
Mechanism of Action: Levitra is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. Nitric oxide then activates the enzyme guanylate cyclase, which results in increased levels of cGMP. Cyclic guanosine monophosphate causes smooth muscle relaxation in the corpus cavernosum thereby allowing inflow of blood; the exact mechanism by which cGMP stimulates relaxation of smooth muscles has not been determined. Phosphodiesterase type 5 is responsible for degradation of cGMP in the corpus cavernosum. Levitra enhances the effect of NO by inhibiting PDE5, thereby raising concentrations of cGMP in the corpus cavernosum. Levitra has no direct relaxant effect on isolated human corpus cavernosum and, at recommended doses, has no effect in the absence of sexual stimulation. Levitra has a greater selectivity for PDE5 versus PDE6, an enzyme found in the retina and involved in phototransduction. Sildenafil, another PDE inhibitor, has a lower selectivity for PDE5 vs PDE6 and is associated with abnormalities related to color vision with higher doses or plasma concentrations of the drug.