The China State Intellectual Property Office (SIPO) has declared the patent for Viagra, the US-based pharmaceutical company Pfizer Inc's erectile dysfunction-correcting drug, as invalid in China because it doesn't conform with Article 26 of China's Patent Law.

Sources from SIPO confirmed this to China Daily Thursday without providing further comment.

In accordance with the law, a company applying for a patent must provide a description of the drug "in a manner sufficiently clear and complete so as to enable a person skilled in the relevant field" to understand the drug.

The abstract shall state the main technical points of the invention or utility model."

In a statement concerning the ruling , Pfizer Inc said it will appeal the board's announcement on Viagra (active ingredient sildenafil).

The decision by SIPO's Patent Reexamination Board overturns the sildenafil-use patent issued in China in September 2001, the company said in the statement.

Pfizer saidthe patent remains in effect until the issue is resolved by a court.

But according to Article 47 of China's Patent Law, any patent right which has been declared invalid shall be deemed to be non-existent.

Article 46 of China's Patent Law, said where the patentee or the person who made the request for invalidation, is not satisfied with the decision of the Patent Reexamination Board declaring the patent right invalid or upholding the patent right, a party may file suit in the people's court within three months.

Viagra entered the Chinese market in July 2000.

Many domestic companies opposed the patent because drugs produced by some Chinese companies had already been using the active ingredient of Viagra in drugs, Sina.com.cn news reported.

Chinese laws allow patent opposers to file complaints to authorities.

The grant meant that until 2014, any domestic companies which use the ingredient "sildenafil citrate" to produce drugs remedying erectile dysfunction would be regarded as patent violaors. In October 2001, 12 domestic pharmaceutical companies requested SIPO to cancel the patent rights, the website news said.

Source: China Daily