The Patent & Trademark Office will re-examine the validity of a Pfizer Lipitor patent covering a crystalline form of atorvastatin.

PTO will consider whether the 44 claims in the patent (no. 5,969,156) were disclosed in two earlier patents covering the statin.

On Dec. 2, PTO granted the re-examination request filed by the Public Patent Foundation in September. PubPat asserted that all of the claims in the '156 patent are invalid in light of two earlier patents (nos. 5,273,995 and 5,686,104).

PTO said PubPat's re-examination request raised "a substantial new question of patentability" affecting the '156 patent.

"Specifically, prior art references" of the '104 and '995 patents "teach different forms of Lipitor not considered during prosecution" of the '156 patent, PTO said.

The agency's decision to re-examine the patent is not expected to pose a threat of near-term generic competition for the blockbuster cholesterol agent. Nevertheless, it could affect how long Pfizer can keep Lipitor generics off the market.

The '156 patent is one of five Lipitor patents listed in FDA's "Orange Book." It is the latest-expiring of the five, running until January 2017 following a six-month pediatric extension. The patent issued in October 1999.

Pfizer said the '156 patent is not one of the two main Lipitor substance patents, which are currently the subject of a bench trial in Wilmington, Del. federal court.

In that trial, Pfizer and Ranbaxy are litigating infringement and invalidity claims relating to the '995 patent, which expires in June 2011, and patent no. 4,681,893, which expires in March 2010. The '893 has the earliest expiration of the five listed patents.

Pfizer said Ranbaxy was the first ANDA filer on both patents. The bench trial began Nov. 30 is expected to conclude the week of Dec. 13, Pfizer said.

The company said it believes the '156 patent is "solid" and that PubPat's challenge does not raise any new legal questions.

Third-party requests for re-examination such as the one PubPat filed "are successful in having the subject patent either narrowed or completely revoked roughly 70% of the time," the foundation said.

Pfizer can submit a statement in the re-examination proceeding by Feb. 2, and PubPat can submit its own reply two months after Pfizer's filing.

- Sue Sutter

PTO Reconsidering Validity Of One Of Pfizer’s Lipitor Patents

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