Ranbaxy Laboratories said the Federal Court of Canada granted it a favorable decision in a case against Pfizer, finding one of Pfizer’s Canadian atorvastatin patents invalid.The setback for Pfizer could mean generic Lipitor becomes a target for importation into the US, depressing sales of the drug in its most lucrative market, The Wall Street Journal reported.The decision came after the court denied a Pfizer request to block approval for a generic version of Lipitor, the world’s best-selling drug. Pfizer said it will appeal.The ruling involves a patent covering the calcium salt of atorvastatin, the active ingredient in Lipitor, which was set to expire in July 2010.Honorable Justice von Finckenstein dismissed Pfizer’s move because the patent did not correctly and fully describe the invention. The judge upheld another Pfizer patent, which protects Lipitor only until May of this year.The ruling on the calcium salt patent has no immediate commercial impact, Pfizer said, because Ranbaxy is subject to other pending patent litigation with Pfizer. But the firm faces a real threat if generic exposure comes years before the projected 2010 expiry.”Lipitor is such a staple of so many Americans’ daily therapeutic regime that its availability [as a generic] across the border could facilitate pricing pressures in the US to prevent widespread trafficking from Canada, beyond direct purchasing by US citizens,” Lehman Brothers’ Tony Butler wrote in a note to investors Friday, the Journal reported.