Less than a fortnight after winning a famous patent victory that protects Plavix, Sanofi-Aventis has received a fresh boost with the news that a generic version of its biggest earner, the blood thinner Lovenox, will not be hitting the US market anytime soon.

In a filing to the US Securities and Exchange Commission, Momenta Pharmaceuticals revealed that completion of a review of its generic version of Lovenox (enoxaparin) by the US Food and Drug Administration is going to take longer than it first thought. Momenta had originally expected the agency to take about 18 to 24 months from when it filed an Abbreviated New Drug Application for M-Enoxaparin (with its partner, Novartis’ Sandoz unit) in August 2005 to make a decision.

Now, however, any decision will "likely extend beyond its prior guidance” because of what the firm says is “a change in the projected timing of certain activities required for the completion of the FDA's review of the ANDA”. Momenta declined to say any more and did not provide a new projection for the timing, adding that the FDA review "continues to progress satisfactorily”, but analysts fear that the delay could be anything from a few months to three years. Investors are also worried and Momenta shares closed down over 9% to $10.28.

Momenta’s loss is Sanofi’s gain though it still faces a lot of pressure in defending Lovenox. In February, a court in California ruled against the firm in its patent infringement lawsuit against Amphastar Pharmaceuticals and Teva Pharmaceutical Industries which are seeking approval from the FDA to sell a generic version of the antithrombotic and those two firms filed ANDAs more than two years before Momenta. On the plus side for the Franco-German drugmaker, however, is the fact that Lovenox is a quasi-biological product so any review of a copycat version will be extremely forthright.

Good news then for Sanofi, which has been floundering somewhat since an FDA advisory panel unanimously recommended against approval for its obesity drug Acomplia (rimonabant) at the beginning of the month. However competition for Lovenox, which had sales of 634 million euros (+8.2%) in the first quarter, is looming, notably in the form of GlaxoSmithKline’s Arixtra (fondaparinux sodium).