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The search for the perfect impotence drug won't end soon

May 18, 2009 |  1:08 pm

ViagraTaking Viagra, Levitra or Cialis improves erectile function. That much we now know. Again.

What we still don't know is which medication works best.

At the request of the American College of Physicians, the Agency for Healthcare Research and Quality, part of the U.S. Department of Health and Human Services, set out to assess the impotence drugs' effectiveness and their risk of side effects. Doctors apparently like to have as clear a picture as possible before prescribing the drugs to patients.

The report, released today, distills evidence from 126 randomized controlled trials of the drugs technically known as oral phosphodiesterase type 5 inhibitors. But only four trials compared sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis) against each other, making cut-and-dried conclusions difficult.

Researchers have a pretty good idea of the drugs' benefits. And of their risks -- most common are headaches, flushing, dyspepsia (indigestion -- here's an explainer from MedicineNet) and rhinitis (inflammation of the nose's inner lining -- and another explainer). They just can't tell doctors which one should be prescribed. 
 
But the report does offer one-place-shopping for information on dose-response effect of the individual drugs (higher doses tended to get better results), plus less-conclusive assessments of injections, suppositories, topical treatments, hormones and drugs prescribed off-label. The researchers also tried to evaluate the usefulness of routine blood tests in identifying (and thus, treating) hormonal disorders. The limited amount of data made this problematic.

For most men, and their doctors, the report largely means: If you're looking for a thorough comparative summary of the data on these drugs, now you have one.

Of note, the big three drugs tended to work fairly well across the board. That is, they helped men regardless of the cause of erectile dysfunction. (Here's a primer on causes, courtesy of the Urology Channel.)

And men tended to prefer tadalafil (Cialis) over its cousins, partly because the drug's effects last longer.

The researchers wrote: "There is still insufficient information regarding the effectiveness and safety related to the use of different treatment modalities in various clinical subgroups of patients (e.g. diabetes, cardiovascular disease). Furthermore, there is insufficient data with regard to long-term adverse effects of oral ED medications that have been used by millions of users for over a decade."

Translation: We need more data, especially about how the drugs might affect men with diabetes and heart disease. And long-term data -- we definitely need more of that.

-- Tami Dennis

Photo: Viagra has been often discussed, but not often compared -- clinically speaking -- to its cousins Levitra and Cialis.

Credit: AFP / Getty Images

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