Pfizer said yesterday that the US Patent Office had backed the validity of a patent on its top-selling drug Lipitor (atorvastatin calcium).

In doing so the USPTO has reversed an earlier decision invalidating the patent, covering the crystalline form of Pfizer’s cholesterol-lowering agent. The agency has been reviewing the patent, which expires in 2017, following a legal challenge from the nonprofit Public Patent Foundation (PUBPAT).

Earlier this year, the USPTO came down on the side of PUBPAT, which is an organization specifically set up to challenge what it regards as incorrectly awarded patents.

For its part, PUBPAT also claimed victory in the case, saying that Pfizer had agreed to ‘significantly narrow the patent to specifically exclude the form of atorvastatin tested in its early clinical trials for Lipitor’.

The organization says the patent is the only one asserted by Pfizer in roughly two dozen patent infringement lawsuits filed last year against websites selling generic atorvastatin to Americans.

Pfizer said that the patent office decision regarding the crystalline form of atorvastatin used in Lipitor is distinct from the ongoing patent litigation with Ranbaxy in the USA, which involves the basic and enantiomer patents that provide market exclusivity for Lipitor through March 2010 and June 2011, respectively.

European challenges

Meanwhile, two generic companies have challenged Pfizer's patents for Lipitor in Spain, where it is sold as Zarator.

Ratiopharm of Germany and India's Ranbaxy Laboratories are claiming that Pfizer is not entitled to exclusivity in Spain for Lipitor, even though the patent for the products does not expire there until 2010.

Pfizer has been defending various actions over the same question in courts in the UK, Norway and Austria. The company won its cases in Norway and the UK, while Ranbaxy received leave to appeal the decisions, but lost in Austria.

Ratiopharm has asked a court in Madrid to rule that patent number ES 2167306, which expires in July 2010, is invalid. This case has been going through the courts since 2003, while Ranbaxy started its litigation more recently in a commercial court in Barcelona.