* Confident questions raised can be promptly addressed
FRANKFURT, May 28 (Reuters) - Bayer (BAYG.DE: Quote, Profile, Research, Stock Buzz) and Johnson & Johnson's (JNJ.N: Quote, Profile, Research, Stock Buzz) said on Thursday the U.S. Food and Drug Administration declined to approve their experimental blood thinning pill Xarelto, asking for more information.
In a so-called "complete response letter" the FDA has, however, not requested that any new clinical or non-clinical studies be conducted to evaluate the drug -- known scientifically as rivaroxaban -- the companies added.
The drug is already approved in Europe to prevent blood clots after major orthopaedic surgery, and the two companies are also seeking clearance for the potential blockbuster in the United States, its largest market.
The pill was backed by an FDA advisory committee in March for use in knee and hip replacement patients despite concerns over possible side-effects and worries about long-term use.
The drug's blockbuster potential lies in the planned use to prevent strokes in patients suffering from atrial fibrilation, a common form of irregular heartbeat, with market launch not seen before 2011.
In its use after orthopaedic surgery, the oral drug is a rival to Sanofi-Aventis' (SASY.PA: Quote, Profile, Research, Stock Buzz) injectable treatment Lovenox, a standard treatment based on heparin.
Bayer's privately-held German rival Boehringer Ingelheim said it is about one and a half years ahead in the race to bring its blood-thinning pill Pradaxa to the mass market of stroke prevention but analysts say it remains open to question how it will fare against Xarelto.
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