U.S. drug safety regulators are coming under fire for their response to years of suspicions, confirmed last week, that arthritis drug Vioxx increased the risks of heart attacks and strokes.

Merck & Co. Inc.‘s withdrawal of Vioxx Thursday raised inevitable questions about whether the prescription drug taken by millions should have come off pharmacy shelves sooner, or at least carried stronger warnings.

Amid “mounting evidence over five years that this drug had cardiovascular risks, the (Food and Drug Administration) settled for almost a minimal amount of action, a small change in the product labeling,” said Thomas Moore, a health policy analyst at George Washington University.

The FDA should have given “a more prominent and clear warning,” Moore said.

Dr. Eric Topol, a cardiologist who warned about heart risks from Vioxx in 2001, charged the FDA with “considerable failings” in its handling of the case.

From the drug’s approval in 1999 until its withdrawal, the FDA “could have exerted more effect on Merck’s progress with Vioxx,” said Topol, head of cardiovascular medicine at the Cleveland Clinic.

The agency could have requested a one-year study in people at highest risk for heart problems, or advised doctors against prescribing Vioxx to anyone with heart disease, Topol said.

The criticism follows recent charges that the FDA was slow to react to another risk - a link between pediatric antidepressant use and suicidal behavior. Concerns arose in May 2003, but only last month did FDA officials conclude there was a link between the drugs and suicide attempts by kids.

The FDA was “concerned and aware of the potential for cardiovascular effects with (Vioxx) for quite a few years,” acknowledged Steven Galson, acting director of the FDA’s Center for Drug Evaluation and Research.

The risk was not fully clear until last week when Merck announced a three-year study of 2,600 patients showed those who took Vioxx were more likely to suffer heart attacks and strokes than others who took a placebo, FDA officials said.

Galson said the FDA acted appropriately by ordering Merck to add information in 2002 about a study in 2000 that showed an elevated cardiovascular risk for Vioxx patients compared with others who took the generic painkiller naproxen.

The FDA also was watching reports of heart attacks and strokes in Vioxx users after the drug was being sold. Because those conditions are so widespread it was “almost impossible” to determine which were caused by the drug, Galson said.

Some cardiologists defended the FDA’s handling of Vioxx. “The information before this was so sketchy,” said Dr. Robert Bonow, chief of cardiology at Northwestern University.

The FDA review system is not designed to catch all serious risks before drugs hit the market. Less common problems only show up after a medicine is sold widely. FDA officials say they are working to improve monitoring of side effects once drugs are on the market.

But Moore said the Vioxx case illustrated a breakdown of the drug safety system because long-term safety studies were not done after the cardiac risk first was suspected.

“The result of this is literally millions of people wake up one morning and discover they were taking a drug that did more harm than good,” Moore said.