WASHINGTON (AP) -- Many men may be taking Viagra to treat impotence that was caused by other pills such as antidepressants and blood pressure drugs, raising the question of whether some could be cured simply by adjusting their prescriptions.
The consumer group making that point Wednesday also cited 174 reports of Viagra users suffering side effects, including 31 deaths, in petitioning the government to strengthen Viagra's safety warnings.
The Food and Drug Administration remains convinced that Viagra is safe when used by the right men, but said it will consider Public Citizen's concerns.
The drug's label already warns doctors not to prescribe Viagra to men who take nitrate-containing drugs such as the heart medicine nitroglycerin, because the mix can kill -- and apparently has killed a few men. The FDA also warns that the sudden sexual exertion may be too risky for some heart patients.
Pfizer spokeswoman Mariann Caprino said, "There are no new trends that have emerged that would warrant a change in the product's label."
But Public Citizen discovered that manufacturer Pfizer Inc. had refused to admit into clinical trials of Viagra any men with certain heart-related conditions. Yet men with those same conditions are allowed to take the drug today, and some have suffered heart attacks or strokes.
That's a dangerous double-standard, the advocacy group charged. It urged the FDA to immediately forbid Viagra's use by men with those risk factors.
"They designed studies to minimize the chance this drug would have adverse events, and then they threw these people with high risks back in the pool when the drug was approved," said Public Citizen's Dr. Sidney Wolfe. "FDA needs to get a significant amount of blame for allowing" that.
In addition, the FDA should warn doctors to check whether a man's impotence is a side effect of one of more than 60 other drugs known to cause sexual dysfunction before they prescribe Viagra, a $10-a-pill therapy that can cause its own side effects, Wolfe said.
"Most doctors are not even remotely aware of this long list of drugs that can cause or worsen impotence," he said. "It may be possible to lower the dose or switch to something else. ... Those things are worth trying with these stakes."
But diagnosing drug-induced impotence can be difficult, and not every man who does suffer it can switch medicines, warned FDA drug chief Dr. Robert Temple.
As for Wolfe's other complaint, the FDA does not routinely forbid people from using a new drug just because they have health risks considered troublesome when the drug was undergoing testing, Temple said.
However, some men with heart-related problems may not be good candidates for Viagra, the FDA official cautioned. The FDA already warns that for some men, having sex could be just as big a risk for a heart attack as, say, shoveling snow because they're not up to the exertion. The doctor must make an individual evaluation.
"That's the question that's always been: Are these adverse events really related to the drug or to a higher rate of activity than the person's used to?" Temple said.
Wolfe cited risk factors including: a heart attack or stroke in the last six months, heart failure, unstable angina, an abnormal electrocardiogram, certain arrhythmias or low blood pressure. Wolfe also said Viagra can inhibit blood clotting and so men taking blood thinners or who have ulcers or bleeding disorders should not take it -- they, too, were considered too risky to participate in Viagra's testing.
Wolfe analyzed 174 reports of side effects, including 31 deaths, filed with the FDA since Viagra began selling three months ago. There is no way to prove Viagra is to blame for the individual cases, and the FDA says it sees no unexpected problems from the drug so far.
But Wolfe said that among the patients known to take additional medication, 46 percent take a drug that can cause sexual dysfunction, which he called unacceptably high.
Wolfe listed more than 60 drugs, including the heart medicine Adalat, the antidepressants Prozac and Zoloft and dozens of blood pressure drugs, that can cause sexual side effects, urging the FDA to educate doctors and patients about the problem.
And by looking at what medicines the men were taking, he estimated that over a third had risk factors that would have excluded them from Viagra's clinical trials.