Barr Laboratories says that it has initiated a challenge to the US patents that cover Sanofi-Aventis’ colon cancer drug Eloxatin.

The generics firm has filed an Abbreviated New Drug Application for its copy of Eloxatin (oxaliplatin) with the US Food and Drug Administration and its submission contains a paragraph IV certification. Because of this, Sanofi and privately-held partner Debiopharm of Switzerland, were informed of the ANDA filing and the two firms promptly filed suit in the New Jersey District Court to prevent Barr from getting its generic onto the market.

Eloxatin, which is given by injection, is used to treat stage III colon cancer patients who have undergone complete removal of their primary tumour, and also as a treatment for advanced cancer of the colon or rectum.

The importance of Eloxatin to Sanofi’s fortunes is considerable. It had sales of approximately $1.1 billion in the USA, based on IMS data for the 12 months ended October 2007. Total third-quarter revenues for the drug were 383 million euros, which was down 4.5% as a result of the generic competition that the drug is already facing in Europe.