Pfizer has successfully defended its top-selling cholesterol-lowering drug Lipitor (atorvastatin) from a patent challenge in Norway by Indian drugmaker Ranbaxy Laboratories.

Pfizer said yesterday that the Oslo District Court ruled that one of its patents - covering an intermediate compound used to make atorvastatin - would be infringed if Ranbaxy went ahead with marketing its proposed generic atorvastatin product.

Last month, Ranbaxy lost a similar lawsuit concerning generic atorvastatin in the UK as Pfizer continues to defend its European Lipitor franchise [[13/10/05a]], although the Indian firm has said it will take this case to appeal [[04/11/05h]].

“Ranbaxy can appeal the decision, but it will not be able to market a product made using the patented intermediate compounds unless it prevails on appeal,” said Pfizer in a statement.

Pfizer said the court also ruled separately that another Pfizer patent, covering a process for converting crystalline atorvastatin to amorphous atorvastatin, is valid but not infringed by Ranbaxy in Norway.

Lipitor's main patent is not due to expire until 2011 and, with the drug soon expected to reach $12 billion dollars in annual revenues, the US giant is determined to maintain exclusivity on its best-selling drug for as long as possible. A lawsuit between Pfizer and Ranbaxy is also ongoing in the USA [[23/96/05b]].