A group of 12 Chinese drugmakers is to appeal a recent ruling that reinforced the patent armour of Pfizer’s billion-dollar erectile dysfunction drug Viagra in China, according to media reports.

Earlier this month, a Chinese court overturned a previous decision made in 2004 that rendered Pfizer’s intellectual property for a certain ingredient in Viagra (sildenafil citrate) invalid, effectively opening up the market to copycat versions of the drug.

The decision on June 2 to uphold Viagra’s patent falls in line with China's stated intention of improving the intellectual property environment in a country renowned for counterfeit goods.

But those companies squaring up to Pfizer seem certain that the appeal will go in their favour. “I am positive of the result based on the evidence provided by the office,” Wang Wei, a Beijing Huake Union Patent Office lawyer who represents the companies told Reuters, adding: “It might take three to five months for the court to make the decision.”