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| Male Sexual Dysfunction |
| The Massachusetts Male
Aging Study, published in 1994, reported that in men between the ages of
40 and 70, the probability of complete impotence tripled, from 5 percent
to 15 percent, while the chance of moderate impotence doubled, from 17
percent to 34 percent. More than half of American men over age 40 -- over
28 million individuals -- may have some degree of erectile dysfunction.
Traditionally the term "impotence" has been used to describe a man's inability
to attain or maintain an erection sufficient for sexual intercourse; urologists
and other experts in the field, however, now prefer the term "erectile
dysfunction."
In healthy men, an erection is a vascular response that is mediated by a complex series of events triggered by sexual stimulation. In the flaccid state, the muscles of the penis are contracted. When sexually stimulated, the brain sends signals carried by neurotransmitters, or chemical stimuli, that cause the muscles in the penis to relax. Blood fills two cylinders of sponge-like tissue, known as the corpora cavernosa, and the penis becomes erect. In men with normal erectile function, the penis is composed of 42% to 53% smooth muscle. As men age, blood flow to the penis may decline causing the normal structure of the penis to change; smooth muscle may be replaced by fibrous tissue that cannot expand sufficiently to initiate and maintain an erection. Symptoms of erectile dysfunction typcially begin when smooth muscle in the penis falls below 42%. Historically, drug therapy for the treatment of male sexual dysfunction consisted of delivering vasoactive drugs directly to the penis via injection and, more recently, via the urethra. In 1998, the U.S. Food and Drug Administration (FDA) approved Viagra (sildenafil), the first oral medication for erectile dysfunction. In men, as smooth muscle is lost, impotence worsens. For approximately 50% of the impotent population, sufficient smooth muscle remains for oral therapies such as Vasomax or Viagra to provide clinical benefit. As the condition in men worsens, direct administration of vaso-active drugs injected into the penis are required to have benefit in restoring penile function. Roughly 30% of men with impotence require penile injections in order to achieve rigid erections. In the most severe cases, 20% of impotent men, penile implants are required.
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Oral vaso-active drugs can improve sexual function by directly
or indirectly addressing the blood flow to the genitalia via several different
biologic pathways. Two physiological systems, the sympathetic and the parasympathetic,
play a role in sexual response. Currently there are existing drugs, as
well as new products in development, that can take advantage of either
system. Alpha adrenergic blockers, such as Vasomax (phentolamine mesylate),
may produce an effect in as little as 15 to 20 minutes. Drugs that inhibit
the enzyme phosphodiesterase generally require about one hour or more to
take effect. In both cases, sexual stimulation is necessary for a normal
response.
The Journal of the American Medical Association recently published a report on a representative sample of approximately 1,500 women in the United States that revealed that approximately 64% of all women in a relationship at some point experience arousal or orgasmic dysfunction. The preponderance of those reporting such dysfunctions were not post-menoposal women, but rather such experiences were fairly evenly distributed among women ranging from 18 to 59 years of age. Despite its prevalence, the understanding of female sexual dysfunction is not nearly as advanced as its male counterpart. Female sexual disorders include lack of desire, arousal disorder (problems with lubrication and sensation), anorgasmia, pelvic pain disorder and vaginismus (involuntary contraction of vaginal muscles). A recent upsurge in interest has led to a better understanding of female sexual anatomy. Treatment for female sexual dysfunction has traditionally involved psychological
intervention or hormone replacement therapy. With the success of vasoactive
drug therapy for men, however, drugs that increase blood flow to the genitalia
may prove useful therapeutic strategies for women. Currently both alpha-blockers
and phosphodiesterase inhibitors are being evaluated for the treatment
of female sexual dysfunction.
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