The opinion was provided at the request of a Spanish court that is hearing a patent infringement case filed against Pfizer by generic manufacturer Ranbaxy.
The patent office rejected arguments by Ranbaxy that a patent covering atorvastatin calcium, the active ingredient in Lipitor, is invalid for lack of novelty and lack of inventive step. The opinion will be among several expert views the court will consider before rendering a decision in the pending litigation.
Lipitor is a cholesterol lowering drug and is sold in Spain under the brand names Zarator and Cardyl.
Pfizer has already received favorable decisions favoring their Lipitor patents in Austria, the Netherlands, Britain and Norway.
In another case involving the atorvastatin calcium patent, the Court of Appeal in Madrid has rejected an appeal filed by generic manufacturer Ratiopharm.
Pfizer said it will continue to vigorously defend its intellectual property rights against infringement.