Pfizer has filed an appeal after losing a lawsuit over rights to the Chinese name given to Viagra, its treatment for erectile dysfunction.

The world's largest drugmaker had previously sued Guangzhou Welman Pharmaceutical of China over its usage of the brandname ‘Wei Ge,’ which means ‘Mighty Brother’ in November 2005, but lost the case last month. Pfizer markets Viagra (sildenafil) as ‘Wan Ai Ke’ in China, but it is known as Wei Ge by the public at large.

Welman had applied to register the Wei Ge name in 1998, the year Pfizer launched the blockbuster in the USA, though the company only received its Chinese patent for Viagra in 2001.

In announcing its intention to appeal, Pfizer said the ruling by the Beijing First Intermediate People's Court “fails to support Chinese efforts to create an environment of innovation that provides consistent protection of intellectual property rights for companies bringing new medicines to China."

Despite the setback over the name, Pfizer has won some important victories in the Chinese courts recently. In December, a Beijing judge upheld Pfizer's Chinese patent for Viagra and ordered two local rivals to stop making generic versions, also sold under the name Wei Ge.

Last summer, a group of 12 Chinese drugmakers appealed a ruling that reinforced the patent armour of Viagra in China, after a court overturned a previous decision made in 2004 that rendered Pfizer's intellectual property for sildenafil invalid, effectively opening up the market to copycat versions of the drug.