Pradaxa has become a blockbuster drug in its two years on the market, bringing in more than $1 billion in sales for its maker, the privately held German drug maker Boehringer Ingelheim.

But Pradaxa has been linked to more than 500 deaths in the United States, and a chorus of complaints has risen from doctors, victims’ families and others in the medical community, who worry that the approval process was not sufficiently rigorous because it allowed a potentially dangerous drug to be sold without an option for reversing its effects.

Pradaxa is an example, some critics say, of what can happen when a drug that performs well in tightly controlled trials is released into the messy world of real-life medicine. Boehringer Ingelheim said it was working on developing an antidote but that even without one, patients in a large clinical trial died at roughly the same rate as those who were taking warfarin.

The Food and Drug Administration released a report on Friday that found that the drug did not show a higher risk of bleeding than for patients taking warfarin. The report did not address the lack of an antidote for Pradaxa.

“The evolving spontaneous reporting patterns do not indicate a change in the favorable benefit-risk profile of Pradaxa, when used correctly according to the approved label,” Boehringer Ingelheim said in a statement. In other words, the drug is still safe. But some reports have indicated that doctors are not sufficiently cautious when prescribing Pradaxa, giving the drug to older people or those with kidney problems even though there is evidence that the bleeding risks are higher in those groups. The company recommends testing patients’ kidney function before prescribing Pradaxa and notes that the risk of bleeding increases with age.