New Therapies for Erectile Dysfunction

Ira D. Sharlip, MD

Disclosures

August 06, 2003

Question

How are the new phosphodiesterase inhibitors different from sildenafil?

Response from Ira D. Sharlip, MD

In 2003, two new oral phosphodiesterase inhibitors for the treatment of erectile dysfunction (ED) became available in Europe and other countries and are expected to be approved in the United States. They are vardenafil (Levitra), developed by the Bayer Corporation and co-marketed with GlaxoSmithKline; and tadalafil (Cialis), developed by Lilly/ICOS. Vardenafil and tadalafil join sildenafil (Viagra) from Pfizer as the only effective oral therapy for the treatment of ED. Sildenafil, vardenafil, and tadalafil are highly specific inhibitors of type 5 phosphodiesterase, so that the mechanism of action of all 3 agents is identical. The efficacy of all 3 agents is similar, with about 80% of men stating that these agents produce an improvement in erections and about 75% of men finding that they are able to have intercourse successfully.

The most common side effects of all 3 agents are headache, facial flushing, rhinorrhea, and dyspepsia. While myalgia and back pain can occur as a class effect of all 3 agents, myalgia and back pain seem to be more common with tadalafil, approaching 10% in clinical trials. The cause of the myalgia and back pain is not clear. The best explanation is vascular congestion of the muscles of the back and gluteal regions. Tadalafil has the lowest prevalence of visual side effects among the 3 agents.

While sildenafil absorption is moderately impaired following a high-fat meal, vardenafil and tadalafil can be taken without regard to concomitant ingestion of food or alcohol.

The onset of action of vardenafil and tadalafil is similar to that of sildenafil, at about 30 minutes. The half-life of vardenafil is similar to sildenafil, at about 4 hours, but the half-life of tadalafil is distinctly different, at 17 hours. Related to the half-lives of the 3 agents, the duration of action of sildenafil and vardenafil is about 4-6 hours, while the duration of action of tadalafil is about 36 hours. The greater duration of action of tadalafil may be either an advantage or a disadvantage, depending on an individual patient's pattern of sexual activity. For those men who want to be sexually active more than once in a 36-hour period, the longer duration of action of tadalafil is an advantage. But for men who develop angina and therefore might require treatment with an organic nitrate (such as nitroglycerine, which is absolutely contraindicated for 24 hours after a dose of sildenafil or vardenafil and for a longer but unknown period after a dose of tadalafil), the longer duration of action is a disadvantage.

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