Pfizer, the US pharmaceutical company, said on Monday(Aug 15 2011) that it had won a closely watched patent case against Teva Pharmaceutical Industries​ that would block the generic drug maker from selling an unbranded version of its blockbuster drug Viagra next year.

Viagra, which treats erectile dysfunction, generates about $1bn in annual revenues for Pfizer, which is already facing the loss of its exclusive rights to sell Lipitor, its top selling cholesterol drug, in November. A federal court in Virginia ruled that Pfizer’s patent gave it exclusive rights to sell Viagra until 2019.

The drug compound behind Viagra, which was initially intended to treat High Blood Pressure, was originally set to expire next year. Pfizer was granted a new patent 10-years ago to cover the drug’s use for treating impotence.

Teva and other generic drug makers had questioned the validity of the second patent in hopes of being able to sell the popular drug sooner.

“We are pleased that the court recognised the validity and enforceability of our Viagra patent for the treatment of erectile dysfunction,” Amy Schulman, executive vice-president and general counsel for Pfizer, said in a statement. “Protecting the intellectual property rights of our innovative core is critical, and Friday’s court decision acknowledges Teva’s clear violation of our patent rights.”