Sexual healing

 作者:秋阳榴     |      日期:2019-03-08 01:16:09
By Nell Boyce SEX sells. It may be a cliché, but given the astonishing impact of Viagra, few can disagree. This diamond-shaped blue pill so dominated the scene in 1998 that even the Nobel Prize in medicine was billed by many newspapers as honouring the discovery that led to Viagra. In fact, the Nobel prizewinners showed that nitric oxide dilates blood vessels, and does so by stimulating production of a smooth muscle relaxant called cGMP. Viagra, developed by researchers working for the drugs company Pfizer in Sandwich, Kent, works by blocking an enzyme called phosphodiesterase that breaks down cGMP. The resulting increase in blood flow to the penis allows two-thirds of previously impotent men to achieve an erection. But this discovery was an accident, made in 1992 during a trial of the drug then known as UK92-480, as a treatment for angina. Pfizer researchers found that many men enrolled on the trial reported improvements in their sex life. Executives at Pfizer’s headquarters in New York City realised that they had stumbled on a potential blockbuster, and switched their focus to the treatment of erectile dysfunction, as impotence is formally known. And when the US Food and Drug Administration (FDA) finally gave Viagra its blessing on 27 March this year, the pill became an overnight sensation, breaking sales records previously held by the antidepressant Prozac. Impotent men rushed to their doctors. Few of them were worried about the side effects reported by Pfizer, including fainting, blue-tinted vision and intense headaches. Although the initial surge in sales is now beginning to subside, at least in the US, doctors have already written more than five million prescriptions. A backlash was inevitable. In May, the American Academy of Ophthalmology warned that Viagra might damage the retina, by inhibiting phosphodiesterase in the eye. “It will be many months or even a year or two before we accumulate enough experience to have an answer,” says Michael Marmor of Stanford University in California. Viagra ran into further trouble in July when the FDA reported 39 deaths among US users. The figure has since risen to more than 130. Some of those who died had taken Viagra as well as nitrates for heart trouble, even though Pfizer warns that it might interact dangerously with these drugs. Used properly, there should be no problem, the company insists. Pfizer officials say that heart specialists share this view. “Fifty per cent of cardiologists in America have written a prescription for Viagra,” says company spokeswoman Mariann Caprino. “That’s a tremendous vote of confidence.” Pharmacologists predict that, despite the side effects, Viagra will herald an explosion in pharmaceutical approaches to the treatment of sexual dysfunction. One drug, currently known as IC351, from Icos, a company in Bothell, Washington state, inhibits phosphodiesterase, but it is specifically aimed at the version of this enzyme found in the penis and so should not disrupt vision. Large-scale clinical trials should start in 1999. Other drugs in the pipeline should not interact with nitrates. One, called phentolamine, produced by the company Zonagen of The Woodlands, Texas, has been shown to help up to forty per cent of men with mild to moderate impotence, with nasal congestion as the main side effect. The FDA and Britain’s Medicines Control Agency are now considering whether to approve it for sale. Another drug, called apomorphine, manufactured by TAP Holdings of Deerfield, Illinois, seems to help around half of impotent men to achieve an erection, although some experience mild nausea. Women may also benefit. Although a majority of postmenopausal women complain of difficulty achieving sexual arousal, the only available treatment is hormone replacement therapy. Increasing blood flow to the vagina and clitoris may help, and Pfizer has set up an ongoing study of Viagra in European women to find out. It expects to have an answer early next year. Laboratory research suggests it might work: in September, Irwin Goldstein of Boston University showed that phosphodiesterase is present in the clitoris. “Viagra has had a revolutionary effect,” concludes Harin Padma-Nathan of the University of Southern California Medical School in Santa Monica,