Sanofi-Aventis is facing a delay in bringing its much-touted obesity drug Acomplia to market in the USA, following a Food and Drug Administration request for more information on the product.

The FDA made its request in an ‘approvable’ letter sent to Sanofi-Aventis at the end of last week, according to a brief statement from the Franco-German drugmaker. The company has not yet divulged what additional information the agency has asked for.

Shares in Sanofi-Aventis slid 3.6% on Friday, and continued to decline this morning as investors digested the news. Acomplia has been tipped as a blockbuster for the company, at a time when it is facing the threat of generic competition to its two biggest-selling products, the antithrombotic drugs Plavix (clopidogrel) and Lovenox (enoxaparin).

Sanofi-Aventis had been hoping to introduce the drug in the USA in the middle of this year, into an underserved market that has been predicted to grow fivefold between now and 2012 to reach $2.5 billion. How long the product may be delayed could hinge on whether the FDA has asked for another clinical trial, or additional information based on trials already carried out.

Rejected for smoking cessation

In addition to the delay in approving Acomplia (rimonabant), the FDA also rejected an application to market the drug to help people stop smoking, although this is considered to be of lesser significance in terms of the overall prospects for the product, though still potentially a half-billion dollar market at peak. Overall, Sanofi-Aventis has said it hopes to achieve $3 billion for Acomplia at peak.

Meanwhile, on the positive side for Sanofi-Aventis, final results from a clinical study of the drug have revealed that about half of the people taking it over a two-year period achieved weight loss of 5% or more. This equated to a “modest but sustained reduction in weight,” said the firm, noting that there were also favourable changes in cardiometabolic risk factors with treatment.

However, the authors of the 3,000-patient study, published in the Journal of the American Medical Association (February 15), said a high drop-out rate limited its value. 50% of those taking the highest dose of Acomplia discontinued treatment.