Pfizer, the world's largest pharmaceuticals company, faced increased competition in China after Beijing yesterday overturned its domestic patent for the main ingredient in Viagra, the erectile dysfunction drug. Pfizer said it would appeal against the ruling, which was also expected to cause concern among trade authorities in the US and the European Union that have been closely following the case. One diplomat in Beijing said it was possible the US and EU would consider retaliation.

Viagra has been viewed as a te st case for the protection of pharmaceutical companies' intellectual property in China. Many foreign drug companies find that their products are routinely copied and counterfeit medicines are widespread. "[Pfizer] is extremely disheartened by this recent action," the company said in a statement. Over the next five years, Pfizer said, the company planned to introduce up to 15 medicines in China to treat medical conditions including cardiovascular, neurological, genito-urinary and ophthalmological diseases. "The company noted that appropriate intellectual property protection is essential to these plans," the statement added. An official at the State Intellectual Property Office said he was unable to say why the patent it granted in 2001 to sildenafil citrate, Viagra's active ingredient, was to be revoked. He added that SIPO might issue an explanation later this week.