Daiichi Sankyo and partner Genzyme Corp are suing Impax Laboratories over the latter’s plans to sell a generic version of their cholesterol drug Welchol in the USA.

Impax has filed an Abbreviated New Drug Application on Welchol (colesevelam) and the US Food and Drug Administration’s acceptance of the submission has prompted Daiichi Sankyo and Genzyme to file for patent infringement in a Delaware court. The two patents involved are to expire in 2014 and 2015, respectively.

Impax believes it is the first company to file an ANDA containing a Paragraph IV certification for the product, which would give its copycat version 180 days of marketing exclusivity. US sales of Welchol reached $308 million for the 12-month period ending November 2009.