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Pfizer, the company that developed the phosphodiesterase inhibitor sildenafil (Viagra), reported last week that efficacy results in women with what has been termed female sexual arousal disorder had been inconclusive and would not support filing for regulatory approval to use the drug in this indication.
In a statement, Pfizer said that several large scale, placebo controlled studies including about 3000 women with female sexual arousal disorder showed inconclusive results on the efficacy of sildenafil (http://www.pfizer.com). The disorder is defined by the American Foundation for Urological Diseases as distress caused by a persistent inability to attain or maintain sexual excitement.
Dr Joe Feczko, president of worldwide development with the company, said in the statement: "FSAD [female sexual arousal disorder] is an emerging area of research and is far more complex than male erectile dysfunction. Diagnosing FSAD involves assessing physical, emotional, and relationship factors, and these complex and interdependent factors make measuring a medicine‚s effect very difficult."
However, he added: "Pfizer has made a number of major contributions to the emerging science of female sexuality. Because of Pfizer‚s innovative research, we now have a better understanding of the biochemical and physiological factors involved in female sexual function."
Dr John Bancroft, director of the Kinsey Institute at Indiana University, Bloomington, said: "I am not surprised by the negative results with Viagra in women." He added: "I would not be surprised if there was a subgroup of women who would benefit from such medication—probably quite a small subgroup. But for most women, the factors which are determining the problem are unlikely to be helped by a phosphodiesterase inhibitor."
Dr Bancroft went on to say: "The recent history of the study of female sexual dysfunction is a classic example of starting with some preconceived, and non-evidence based diagnostic categorisation for women‚s sexual dysfunctions, based on the male model, and then requiring further research to be based on that structure. Increasingly it is becoming evident that women‚s sexual problems are not usefully conceptualised in that way."
In a recent survey of women, his group found that indicators of physiological response during sexual activity, including genital response, lubrication, and orgasm, were not predictive of whether a woman was distressed about her sexual life, whereas more emotional and subjective aspects of the sexual relationship, plus her mental and physical health, were predictive (Archives of Sexual Behavior 2003;32:193-208).
He noted: "Ongoing research at the Kinsey Institute is underlining the fact that for many women, sexual desire and arousal depend on the circumstances being right, and there are many different ways in which they can be wrong."
Ray Moynihan, a journalist based in Washington, claimed last year that female sexual dysfunction was "the freshest, clearest example of corporate sponsored creation of a disease." He argued that to build markets for drugs such as sildenafil among women, companies first required a clearly defined medical diagnosis with measurable characteristics to facilitate credible clinical trials.
"Over the past six years the pharmaceutical industry has funded, and its representatives have in some cases attended, a series of meetings to come up with just such a definition," he said (BMJ 2003;326:45-7).
Dr Bancroft reported that the pharmaceutical industry was now investigating testosterone for women with "low sexual desire." He commented: "Again, I would argue that the evidence indicates the value of testosterone for some women, who are probably particularly (and, possibly, genetically) more sensitive to testosterone effects. Whereas for many women, probably the majority, testosterone will have little effect. The picture is confounded by a generally marked placebo response found in evaluations of such treatments."