What goes up ...


By Nell Boyce in Washington DC THE backlash against Viagra has started. A scientist involved in ongoing clinical trials of the first pill for erectile dysfunction claims the reality doesn’t match the hype surrounding the drug. More worryingly, ophthalmologists are concerned that long-term use could damage eyesight. Viagra dilates blood vessels, allowing more blood to flow into the penis. Since its approval by the US Food and Drug Administration (FDA) on 27 March, Viagra has achieved huge sales for its manufacturer, Pfizer of New York, and saturation media coverage. “The hype that came out was incredible,” says James Barada of the Center for Male Sexual Health in Albany, New York. The clinical studies that convinced the FDA to approve Viagra are published this week in The New England Journal of Medicine(vol 338, p 1397). Viagra significantly improved the quality of men’s erections and quadrupled their success at having intercourse. In one study of 532 men taking either Viagra or a placebo, those receiving 100 milligrams of Viagra doubled their frequency of erections. Among men taking this dose of Viagra, 69 per cent of the attempts at intercourse were successful, compared with only 22 per cent in the placebo group. But many of the men in these studies had achieved intercourse in the previous three months, and so were not clinically impotent, according to Barada. He is now running an eight-week study of Viagra, funded by Pfizer, to see how it compares with other impotence treatments. Barada has written over 150 prescriptions for Viagra and doesn’t dispute that it improves the erections of most men who take it. But of those who are genuinely impotent, rather than merely lamenting the loss of youthful vigour, only a third achieve sufficient hardness to have intercourse after taking the drug. “I consider them Viagra failures,” says Barada. “You don’t take a drug just because it helps a little bit.” Since Viagra doesn’t treat the underlying causes of impotence, the condition will probably continue to worsen until even the highest recommended doses can’t help, Barada adds. Viagra also causes side effects, among them headaches and fainting due to dilation of blood vessels in other parts of the body. These symptoms occur more often as the dose increases. Most men end up taking 100 milligrams of the drug, the highest recommended dose, but there are fears that some are already taking higher doses despite their doctors’ warnings. The most worrying side effect is blue-tinted vision in some men taking Viagra. “Blue vision is a very unusual symptom,” says Michael Marmor, an eye specialist at Stanford University in California, who has seen Pfizer’s data on Viagra. Viagra works in the penis by inhibiting an enzyme called phosphodiesterase. A similar enzyme exists in the cone cells responsible for colour vision in the retina. “Somehow, the way this drug blocks the enzyme in the cone cells leads to the perception of blue,” says Marmor. This has ophthalmologists worried, because people with congenitally abnormal phosphodiesterase suffer irreversible damage to their retinas over time. What’s more, a common cause of impotence is diabetes, which can also damage the retina. Pfizer has issued a statement saying it has “conducted rigorous visual function tests at doses well above those recommended for Viagra. These studies showed no clinically significant effect on vision in either the short or long term.” But the American Academy of Ophthalmologists wants Pfizer to conduct more studies into how Viagra affects vision. “The company has not measured the electrical activity of the cone cells in the long term,
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