A U.S. consumer group said use of Xarelto, a drug used to prevent blood clots following orthopedic surgery, should not be expanded to include stroke prevention because its safety and effectiveness are uncertain.
The consumer advocacy group Public Citizen said in a letter sent to the Food and Drug Administration on Thursday that two proven drugs already exist to treat the condition.
The FDA is slated to decide by early November whether to expand usage of the drug, marketed by Johnson & Johnson and Bayer AG.
Last month, FDA reviewers said for conditions such as stroke, which can cause irreversible harm, new drugs must be shown to be at least as effective as older treatments, and called for the agency to delay Xarelto's approval.
But an FDA advisory panel subsequently voted in favor of recommending approval.
Public Citizen said Xarelto, also known as rivaroxaban, may cause a rebound occurrence of strokes when the medication is discontinued. The group also said clinical trials of the drug were conducted in a manner that favored Xarelto.
Bayer has said it expects more than 2 billion euros ($2.7 billion) in peak annual sales from the product.
Xarelto is one of three new anti-blood-clotting pills expected to replace the decades-old, and potentially dangerous, stroke preventer warfarin.
Analysts estimate the total annual market for such oral drugs to be as high as $20 billion.
Unlisted peer Boehringer Ingelheim in August won European marketing clearance for its rival stroke prevention pill Pradaxa, defending its lead over Bayer in one of the most promising new classes of medicine.
Another rival treatment is Eliquis, being developed by Bristol-Myers Squibb and Pfizer Inc.