GlaxoSmithKline (GSK) has issued an update on US patent litigation regarding Valtrex (valacyclovir), an antiviral drug used for the treatment and suppression of genital herpes, herpes zoster (shingles), and cold sores.

In May 2003, GSK has filed a patent infringement suit, in the US District court of New Jersey, against Ranbaxy alleging that its generic product would infringe GSK's basic "composition of matter" patent (4957924) for Valtrex, which expires in June 2009 (excluding paediatric exclusivity). No trial date has yet been set for this litigation.

On 1st February 2007, Ranbaxy has received FDA approval for its generic valacyclovir product, and notified GSK that it sought to market the product in the USA. GSK will apply to the court for a preliminary injunction prohibiting launch of this product pending completion of the lawsuit.

Under the terms of an agreement between the companies, previously approved by the court, if GSK applies for such an injunction within 45 days, Ranbaxy will not launch its product until the court either rules on the preliminary injunction or decides the pending court case.

GSK remains confident in the strength of its intellectual property for Valtrex, and the product's exclusivity, afforded by the basic "composition of matter" patent to June 2009. Whilst several companies, including Ranbaxy Pharmaceuticals, have filed for US approval of generic valacyclovir, Ranbaxy is the only generic manufacturer to have made a direct challenge to this basic patent.