Pfizer Inc said that a federal court in the middle district of North Carolina has upheld the company's US patent covering amlodipine besylate, the active ingredient in Norvasc, the world's most-prescribed branded medicine for treating hypertension. The generic manufacturer, Synthon Pharmaceuticals, had challenged the patent.

Judge James A. Beaty ruled that the patent (US Patent No. 4,879,303) covering amlodipine besylate is valid and infringed by the generic manufacturer's product. The decision, which is subject to appeal, prohibits Synthon from launching a generic version of amlodipine until September 2007, a Pfizer press release stated.

"The court has affirmed the validity of our Norvasc patent. We will continue to defend against any patent challenges that seek to undermine the incentives established for bringing innovative medicines to patients," said Allen Waxman, Pfizer's general counsel, same Norvasc patent was held in January 2006valid and infringed by Apotex in a decision by the Northern District Court of Illinois.