Galen faces a legal challenge in the US over the patent rights to a product it bought only last month.

The Israeli generics manufacturer Teva wants to market a version of Serafem in 2005 and is going to court to shave two years off the drug current patent.

Galen bought the rights to the pre-menstrual treatment in December 2002 from Eli Lilly for $285 million as part of a spending spree to boost its product range.

Although the drug is a reformulation of fluoxetine (Prozac), which came off patent in 2001, Serafem current patent is valid until 2007. In 2001, the drug generated sales of around $85 million.

The Northern Ireland-based company has been criticised over its disclosure procedure after it came to light that not all investors and analysts had been told about the patent challenge to Serafem.

"We did not believe that it was material enough information to disclose at the time of the deal as we are extremely confident in the strength of our patent position," John King, Chairman of Galen said.

The company also purchased Duricef, a cephalosporin antibiotic, and Moisturel, a skin moisturising cream, from Bristol-Myers Squibb for $40 million.

pharmafocus@pharmafile.co.uk