Mumbai: GlaxoSmithKline Plc has filed a suit in a US court seeking a preliminary injunction to stop Indian drug major Ranbaxy Laboratories from launching a generic version of Glaxo's Valtrex, a drug used for treatment of shingles and herpes.

The company will file the application a New Jersey federal court to block Ranbaxy from selling the product, it said.

The Indian company won US regulatory approval to market valacyclovir hydrochloride tablets on February 1 but Glaxo has been fighting Ranbaxy's plans since May 2003.

The two had a prior agreement under which Ranbaxy would not launch its product until the court either ruled on the preliminary injunction or decided the pending court case if Glaxo applied for an injunction within 45 days, according to Glaxo. Valtrex, it said, is also protected by a basic "composition of matter" patent which valid till June 2009.

Ranbaxy had received US Food and Drug Administration (FDA) approval for its generic product on February 1 and had informed Glaxo that it plans to market the product.

In a statement, Glaxo said it had filed a patent infringement suit in May 2003 against Ranbaxy contending that its generic product would infringe Glaxo's basic ''composition of matter'' patent for Valtrex which, the company said, expires in June 2009.

Glaxo said while several companies have applied for US approval of generic Valacyclovir, Ranbaxy is the only manufacturer to have made a direct challenge to its basic patent. Ranbaxy, however, failed to comment.