Two drug companies, the Bristol-Myers Squibb Company and Sanofi- Aventis, agreed yesterday to shorten the patent protection time on the blood thinner Plavix by a few months after the companies' initial settlement offer was rejected by the Federal Trade Commission and state attorneys general.

A revised settlement, which is under review, would keep a generic version of Plavix, the world's second-biggest drug behind Lipitor from Pfizer, off the market until June 1, 2011, Bristol-Myers said in a statement. The companies' original offer would have set the licensing date at Sept. 17, 2011, at which time Apotex would pay a royalty to distribute the generic drug.

Bristol-Myers said, "There is no assurance that the revised agreement will address all of the concerns of the F.T.C. and state attorneys general, and there remains a significant risk that antitrust clearance will not be obtained."

Bristol-Myers and Sanofi-Aventis filed a patent infringement lawsuit against Apotex, a generic drug maker based in Weston, Ontario, in 2002 in Federal District Court in Manhattan.

Bristol-Myers is under a 10-year court order until 2013 to get approval from the states when it enters into an agreement to settle a patent infringement case. The company was accused of using patents to thwart low-cost rivals for the cancer medicine Taxol and antianxiety drug BuSpar. If the F.T.C. and state attorneys general fail to sign off on a settlement over Plavix, the case will go to trial.

Plavix, jointly marketed by Bristol-Myers and Sanofi, generates $6.2 billion a year as a treatment for patients in the midst of a heart attack or undergoing artery-clearing procedures. The drug, a $4-a-day pill that prevents the formation of blood clots, is the biggest product for the two pharmaceutical companies.