A British court handed down a mixed verdict for Pfizer in a patent dispute, upholding one of the company’s British patents on Lipitor, the cholesterol-lowering medicine, but invalidating a second patent. The ruling will have no practical effect on Pfizer’s control over Lipitor, because the patent upheld by the court expires in November 2011, while the patent that was invalided expires in July 2010.

Lipitor is the world’s top-selling drug, with sales expected to top $12 billion this year, producing almost half of Pfizer’s profits. Next up is a decision in the similar patent suit in the U.S., closely watched since more than 60 percent of Pfizer’s worldwide Lipitor sales come in the United States.

Ranbaxy is arguing in the Delaware case that Pfizer’s basic patents on the active ingredient atorvastatin are invalid claiming that one of the two Lipitor patents does not cover the exact molecular form of atorvastatin that Pfizer sells as Lipitor. Ranbaxy then claims that the second patent, which does cover the exact molecular form, should be invalidated because it does not represent a real advance over the first patent.

Atorvastatin has two key patents that protect its market exclusivity. The composition patent, U.S. Pat. No. 4,681,893, discloses NCE atorvastatin, while U.S. Pat. No. 5,273,995, discloses the enantiomer having the R form of the ring-opened acid of trans-atorvastatin. The basic composition patent covers the racemic mixtures (including Lipitor, which is one of the stereoisomer). The second patent covers the pure isomer (Lipitor, or R-Trans-isomer). The original basic NCE patent expires on May 30, 2006. Pfizer received a Hatch-Waxman patent term extension, to the original patent, which along with a 6-month pediatric extension protects the exclusivity to March 2010. The racemic patent, including a six-month pediatric extension, expires on June 2011.

The patent examiner in the USPTO initially considered the enantiomer patent invalid because the pure enantiomer was found within the basic NCE patent. Pfizer argued that although the pure enantiomer was mentioned in the ’893 patent, the ’893 patent did not teach how to make the pure enantiomer.

Under patent law, one can obtain a patent on a racemic mixture and then later obtain a patent on a pure enantiomer of the compound disclosed in the racemic mixture. The Patent Board of Appeals of USPTO then agreed with Pfizer that the pure enantiomer claimed in the ’995 patent was not anticipated by the ’893 patent but it suggested to the examiner that he might want to consider an obviousness rejection. The same examiner issued the ‘995 patent.

Since the patent on atorvastatin in the U.S. expires in March 2010, patent protection could end a year earlier than expected if the U.S. District Court follows the British court’s ruling.

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