Pfizer’s attempt to get reissuance of a US patent covering its blockbuster cholesterol-lowerer Lipitor has been rejected, though the decision is not the end of the matter.

The US Patent and Trademark Office, based in Alexandria, Virginia, says on its website that it has issued a “non-final rejection'' of Pfizer's request to reissue a patent, one of two that was invalidated by a US appeals court last August because of a “technical defect”. The patent in question would have extended Pfizer's marketing exclusivity for Lipitor (atorvastatin) to June 2011 – the company’s primary patent on the drug, which expires in March 2010, was upheld by the aforementioned court.

Pfizer has not received official notification from the US patent office about this latest development and a company spokesman said that it was not unusual in such situations for a firm to receive an initial rejection from the patent office only to later get it reissued.

The New York-headquartered behemoth can appeal the decision with the US patent office and there could, if necessary, be a further challenge in the courts. However if Pfizer fails to win its case, Ranbaxy Laboratories is waiting in the wings.

The Indian drugmaker was granted 180-day exclusive marketing rights for a generic version of Lipitor and will be hoping that its drug will start to eat into Pfizer’s sales of the drug, which reached $2.7 billion in the second quarter, in 2010 rather than 15 months later. As for Pfizer, that 15-month difference could be worth $6 billion extra in sales.

The two firms have already been involved in a number of legal skirmishes all around the world. Most recently, at the end of July, a Spanish court upheld Pfizer’s patent covering the calcium salt of atorvastatin, while also ruling that a second patent is invalid.