Which medications in the drug class Phosphodiesterase-5 Enzyme Inhibitors are used in the treatment of Erectile Dysfunction?

Updated: Aug 08, 2018
  • Author: Edward David Kim, MD, FACS; Chief Editor: Edward David Kim, MD, FACS  more...
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Answer

Phosphodiesterase-5 Enzyme Inhibitors

At least seven phosphodiesterase (PDE) classes are known, many with subtypes identified by structure and function. PDEs are a diverse family of enzymes that have different tissue distributions and functions but that all exert their effect by lowering intracellular levels of cyclic nucleotides, such as cyclic guanosine monophosphate (cGMP).

PDE5 is cGMP-specific and is a major cGMP-hydrolyzing enzyme in the vascular smooth muscle of the penis. PDE5 inhibitors rely on the role of nitric oxide (NO) in inducing vasodilatation. NO relaxes the smooth muscle of the corpora cavernosa peripherally by stimulating guanylyl cyclase activity, which results in increased cGMP levels; inhibition of PDE5 increases intracellular concentrations of cGMP, which, in turn, induces vasodilation.

Available PDE5 inhibitors include sildenafil, vardenafil, tadalafil, and avanafil. These agents do not directly cause penile erections but affect instead the response to sexual stimulation. Sildenafil was the first to be approved, avanafil the most recent. Although all of these agents inhibit PDE5, the newer drugs in the class are significantly more selective in their inhibition.

Sildenafil (Viagra)

Sildenafil is most effective in men with mild-to-moderate ED. It is to be taken on an empty stomach approximately 1 hour before sexual activity. Sexual stimulation is necessary to activate response. Sildenafil is available as 25-, 50-, and 100-mg tablets.

Vardenafil (Levitra, Staxyn)

Vardenafil is most effective in men with mild-to-moderate ED. It is to be taken on an empty stomach approximately 1 hour before sexual activity. Sexual stimulation is necessary to activate response. Vardenafil is available as 2.5-, 5-, 10-, and 20-mg tablets.

Tadalafil (Cialis)

Tadalafil is a PDE5-selective inhibitor that is chemically unrelated to sildenafil and vardenafil. It is most effective for mild-to-moderate ED of varying etiologies, including both organic and psychogenic causes. May take 30 min prior to sexual activity.

Increased sensitivity for erections may last 36 hours with intermittent dosing. Low-dose daily dosing may be recommended for more frequent sexual activity (eg, twice weekly); men can attempt sexual activity at any time between daily doses. In 2011, tadalafil was also FDA approved for daily use for the treatment of men with BPH, as well as ED.

Tadalafil is available as 2.5-, 5-, 10-, and 20-mg tablets. In patients who respond, coitus has been recorded from 30 minutes to 36 hours after administration.

Avanafil (Stendra)

Avanafil is a PDE5 inhibitor that inhibits cGMP degradation and thereby enhances the effects of NO in smooth muscle relaxation of the corpus cavernosum. May take 30 min prior to sexual activity.


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