A federal court in the USA has upheld Pfizer’s US patent protection for its hypertension drug Norvasc (amlodipine), marking a significant blow to Dutch company Synthon, which is now not able to launch a copycat version until September next year.

The decision, which is subject to appeal, follows a similar ruling earlier this year by a federal court in Illinois against Canadian drugmaker Apotex - currently embroiled in a patent battle over Sanofi-Aventis/Bristol-Myers Squibb’s blood thinner Plavix (clopidogrel) – finding the same patent valid and infringed by the latter group.

And, just last month, a federal court in the USA cleared drug giant Pfizer of infringing a patent, held by Dutch company Synthon, covering a process used in the manufacture of the drug.

Pfizer was accused by the US subsidiary of Synthon of infringing its intellectual property last November. The jury also found that Synthon's patent was invalid on multiple grounds, according to Pfizer.

Norvasc has lost patent protection in a number of markets around the world but is still Pfizer's second-largest product, with sales of $2.34 billion in the first half of this year mainly coming from the US market.