The US Patent and Trademark Office has ruled that one of five key patents covering Pfizer’s multi-billion dollar cholesterol-lowering agent, Lipitor (atorvastatin), are invalid.

The ruling came on the back of a challenge filed last year by the not-for-profit organisation, the Public Patent Foundation, which says it “represents the public's interests against the harms caused by the patent system, particularly the harms caused by wrongly issued patents and unsound patent policy.” The patent office rejected all 44 of the patent’s claims. “Revoking Pfizer’s patent is a critical step towards providing American consumers with access to [Lipitor] at a fair price, which will not only provide substantial economic benefit, but will also improve public health, as even Pfizer admits that many Americans in need of the drug are not getting it,” said Dan Ravicher, PUBPAT’s executive director.

However, Pfizer said that the ruling does not affect the validity of two key patents covering Lipitor, which it claims provide the product with market exclusivity through to March 2010 and June 2011 respectively. These two patents are currently being challenged by Indian generics manufacturer, Ranbaxy Laboratories, and the world’s biggest pharmaceutical company says it is currently awaiting a decision by a Delaware court.

The patent at issue in these patent office proceedings concerns the crystalline form of Lipitor and expires in 2017, Pfizer explained, adding that it would respond to the news in due course. “Pfizer will continue vigorously to defend its intellectual property and the validity of its patents,” the firm said in a statement.

- In other news, Pfizer has begun production of a new product that combines the $11 billion-dollar-a-year Lipitor with torcetrapib, which aims to raise levels of HDL, or “good” cholesterol and reduce the risk of heart disease.