Pfizer loses Viagra patent

Drugs giant Pfizer has lost its exclusive patent on the active ingredient in Viagra, its lucrative impotence treatment.

In a case brought by Pfizer's US competitors Eli Lilly and Icos Corporation, the High Court in London ruled that the 1993 patent on the main ingredient of the drug was invalid.

Other firms can now cash in on active ingredient

The judge said the knowledge on which it was based had been in the public domain and that the patent was stifling research by other companies.

Speaking about the active compound involved, sildenafil citrate, the judge said: "I have come to the view this was not an unexpected discovery.

"On the contrary, it is just what papers written on the subject beforehand would have led those engaged in the field to expect."

Appeal under consideration

Pfizer said the ruling did not involve the basic product patent on the impotency drug, and that this was still in force until 2013.

The New York-based company stressed that it still retains rights over the molecular structure which forms Viagra.

It said it was reviewing the court decision and considering an appeal.

The judge is to hear arguments later on the issue of costs and whether to allow any appeal.

Competition

Drugs makers Eli Lilly and Icos Corporation are trying to produce an impotency drug of their own in a joint venture.

The ruling allows them to use a similar active ingredient in their own product.

Sildenafil citrate enhances the effect of nitric oxide, which plays a key role in creating erections, by inhibiting a chemical which can restrict its action.

In its latest financial results, Pfizer said sales of Viagra were 36% higher at $332m, which represents 6% of its total sales of drugs for human treatment.