Lawyers for

Bristol-Myers Squibb

(BMY) - Get Report

and

Sanofi-Aventis

(SNY) - Get Report

are scheduled to appear in federal court Friday morning in a last-ditch effort to protect the blockbuster drug Plavix from a generic competitor.

They want Judge Sidney H. Stein to issue a preliminary injunction against Canada's

Apotex

, which has been

shipping generic versions of the anticoagulant since late last week. They also want the judge to order a recall of all generic Plavix held by distributors.

Bristol-Myers and Sanofi-Aventis say they need both rulings to avoid further damage to sales of Plavix until the court can rule on their patent-infringement suit against Apotex. Analysts speculate that some wholesalers have received many months' worth of the generic drug.

Attorneys for the brand-name companies doubt that a full patent-challenge trial would be held until January, making the decision on the injunction an important one. Patent-infringement rulings can take months to prepare.

Plavix is New York-based Bristol-Myers' biggest product, accounting for $3.8 billion in sales last year, or 20% of its total revenue. The drug is the second-leading seller for France's Sanofi-Aventis, contributing $2.45 billion to last year's sales, or 7.4% of its revenue.

Without a preliminary injunction, the companies say they would be "irreparably harmed" if Apotex keeps selling low-price copies of Plavix.

"The economic and other consequences from Apotex's launch, now that it is underway, are impossible to reverse fully," the companies say in their Aug. 14 petition to the court. "But the entry of a preliminary injunction would surely lessen the injury -- the sooner the better."

If the judge rejects the bid for a preliminary injunction, analysts says Bristol-Myers faces sharp cuts in sales, profits and its dividend. Sanofi-Aventis holds the patent for Plavix, while Bristol-Myers has the U.S. marketing rights.

Apotex

started selling its generic product last week, betting that the companies wouldn't win their patent infringement case. Apotex calls the Plavix patent invalid and unenforceable.

Still, Apotex is taking a chance with an "at-risk" launch, that is, marketing a generic drug before all legal challenges have been concluded. Under most circumstances, if a company goes this route and then loses in court, it could be hit with triple damages.

But Apotex negotiated a reduction in that penalty to a range of 40% to 50% of Bristol's and Sanofi's lost sales. The terms were part of an agreement signed in March that temporarily halted the patent infringement suit. The deal, later amended, included a promise by Apotex to hold off selling generic Plavix until mid-2011. Bristol-Myers and Sanofi-Aventis agreed to pay Apotex up to $40 million.

The arrangement required approval by both the Federal Trade Commission and states' attorneys general.

Although the agreement was nullified when the attorneys general voted against it last month, Bristol-Myers and Sanofi-Aventis remained bound by the terms.

Meanwhile, they're trying to fight the Apotex drug by offering rebates to managed care companies for Plavix. In their petition for a preliminary injunction, they say rebates are designed to "stem the loss of market share and avoid the loss of patient loyalty."

Still, the brand-name companies are in a bind, says Hugh O'Neill, a Sanofi-Aventis vice president, in comments submitted to the court.

If they cut their Plavix price, they'll lose revenue even if they protect market share. However, if they maintain the Plavix price, they will "undoubtedly" lose market share to the cheaper drug. O'Neill says a hold-the-line strategy could lead to a 70% to 80% loss in sales in the first 60 days that an Apotex product is on the market.