Mumbai: Pfizer Inc.has failed to secure reissuance of a US patent protecting its blockbuster cholesterol medicine Lipitor, opening the generic route open to its Indian rival Ranbaxy Laboratories after the patent for Lipitor expires in 2010.

An initial ruling by the US Patent and Trademark Office would open Lipitor to generic competition in March 2010, when the 'basic patent' for the drug expires, rather than in June 2011, when the 'patent at issue' would expire, the company said in its web site.

This means that Ranbaxy can start making generic versions of Lipitor in 2010. Ranbaxy will have 180-day exclusivity after the patent expires in March of that year, meaning that Ranbaxy will be the only generic drugmaker producing low-cost version of Lipitor. Ranbaxy has scored limited legal challenges in lawsuits initiated by Pfizer against it in several countries.

The rejection of the patent revision could cost the pharma giant at least $6 billion.
New York-based Pfizer still holds its basic Lipitor patent, which protects the world's top-selling drug until March 2010.

Pfizer spokesman Bryant Haskins said an initial rejection from the patent office is "non-final" and "not uncommon." He said Pfizer needed more information before the company could decide on its next move.

Pfizer has also not yet received a letter from the patent office informing the company of the decision, Haskins said.

Last August, the US Court of Appeals for the Federal Circuit invalidated one of two Lipitor 'patents at issue' in a legal fight with generic competitor Ranbaxy Laboratories Ltd., moving up the patent expiration.

Pfizer said the court had invalidated the patent because of a "technical defect" and it would seek to correct the defect at the US Patent and Trademark Office.

After the exclusivity runs out, it's open season for generic drugmakers, and revenue is expected to plunge about 80 per cent from name-brand levels.

The 15-month difference between the two patents means a potential $6 billion in US sales for Pfizer, said an equity analyst. Lipitor is highly profitable with a 90 per cent gross margin.

Lipitor is one of the most successful drugs ever developed. It was the first drug to attain $10 billion in annual sales, and hit its record annual tally of $12.8 billion in 2006.

But sales have been declining since last year, with $6 billion during the first six months of 2007, compared to $6.2 billion during the same period in 2006. Generic pressure from Zocor, a cholesterol-cutting drug from Merck & Co Inc that lost patent pressure in June 2006, has been eroding Pfizer's sales.

Lipitor also competes directly with Vytorin, a combination cholesterol treatment from Merck and Schering-Plough.

The loss of patent protection on Lipitor to generic manufacturers would be cause for concern among investors, who fear that Pfizer has nothing in the pipeline worth the name.