Erectile Dysfunction

Erectile Dysfunction

Asif Muneer, David J Ralph, Nigel Borley
European Endocrine Disease 2007 - Issue I
Published: October 2008
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In 2003, two alternative PDE-5 inhibitors were approved—tadalafil (IC50 0.9nM) and vardenafil (IC50 0.7nM). Comparison of the IC50 values (see Table 1) shows that vardenafil is highly selective for PDE-5 compared with the alternative agents, although this does not necessarily translate into a major difference in the efficacy and overall clinical response. Tadalafil has a half-life of 17.5 hours, which allows for greater spontaneity after drug administration. Vardenafil has a half-life of 4.5 hours, but appears to have a marginally more rapid onset of action. Clinically, there is very little difference between these agents in terms of erectile response, and the main contraindication to all of them is concomitant nitrate use by the patient, which can cause significant hypotension. However, independent comparator trials are still required in order to objectively assess whether there is any clinical advantage of one agent over another.

Table 1: Comparison of the Pharmacokinetics of Three CurrentlyAvailable Phosphodiesterase Type 5 Inhibitors

*Denotes ratio of IC50 for particular PDE enzyme subtype to IC50 for PDE-5.IC50 values obtained from in vitro studies.
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