Pfizer says U.S. Lipitor patent initially rejected

NEW YORK (Reuters) - U.S. patent officials have initially rejected claims for the basic patent on Pfizer Inc's blockbuster Lipitor cholesterol treatment, although the drug maker said on Monday it remained confident the patent would ultimately be upheld.

The patent, which expires in March 2010, will remain valid and enforceable while U.S. officials re-examine it, a process that could take as long as a few years, Pfizer said, allowing the company to maintain its grip on the product and ward off generic rivals over that time.

"Given the process can take an extended period of time, it probably will go past March 2010, so we're not as concerned," Edward Jones analyst Linda Bannister said.

A law firm that has represented generic drug maker Ranbaxy Laboratories Ltd in July requested a re-examination of the basic patent of Lipitor, the world's biggest-selling drug with sales of about $12 billion. Any shortening of Pfizer's exclusive hold on Lipitor would be a blow to the company.

An initial rejection is not unusual, and Pfizer will follow with a response in the next two months, the company said.

"We continue to believe that the basic patent was properly granted and will be upheld on re-examination," General Counsel Allen Waxman said in a statement.

Pfizer also wants U.S. officials to reissue a second Lipitor patent, which could extend its hold on the drug until June 2011.

Pfizer shares were off 11 cents at $23.91 in afternoon trading on the New York Stock Exchange,

(Reporting by Lewis Krauskopf; editing by Maureen Bavdek and Gunna Dickson)