French drugmaker Sanofi-Aventis and US marketing partner Bristol-Myers Squibb have been forced to resubmit an important patent settlement deal with Canada’s Apotex regarding Plavix, after regulators rejected the initial proposal.

Earlier this year, the two companies were able to draw a line under the ongoing patent infringement suit with Apotex, after hashing out a deal that prevents the firm from introducing a copycat version of Plavix (clopidogrel) – a bloodthinner and the world’s second-best selling drug - until 2011, in return for an undisclosed sum.

The settlement was a major relief for both Sanofi-Aventis and B-MS, as Plavix accounts for a sizeable chunk of both their sales. The product contributed 518 million euros to Sanofi-Aventis' fourth-quarter sales of 7 billion euros last year, while B-MS reported Plavix sales of just over $1 billion out of total revenues of $5 billion in the same period.

But deal did not sit too well with the Federal Trade Commission, which says that exclusion payments delay the entry of cheaper generic drugs into the marketplace, raising the costs of drug treatment for patients and healthcare payers. Consequently, the FTC requested that the companies resubmit a modified version of their pact. The revised agreement has since been filed with the FTC, but the companies warned in a statement last week that it may not address all of the issues raised, shedding further doubt on the future of the deal.

Recently, the FTC noted that the top pharmaceutical companies have resumed the practice of paying generic drug manufacturers to keep copycat versions of brandname medicines off the market, despite abandoning the practice in the late 1990s. The agency has successfully discouraged this type of agreement in recent years by filing lawsuits against the companies involved, but recently suffered two defeats on appeal that, it is alleged, have encouraged pharmaceutical companies to adopt the practice once again.