Twelve Chinese pharmaceutical companies are appealing a court ruling that sides with Pfizer Inc. and prevents local drug makers from selling generic versions of Viagra, a state-run newspaper reported.

The companies filed the appeal at Beijing's High People's Court, calling for the reversal of the June 5 decision by a lower court to uphold Pfizer's patent for the impotence drug, the China Daily said.

No date has been set for a hearing of the case, which many view as a litmus test for whether China is committed to protecting intellectual property rights, part of the agreement it made when it joined the World Trade Organization in 2001.

The earlier decision by Beijing's No. 1 Intermediate People's Court overturned a 2004 decision by the patent review board of China's State Intellectual Property Office.

SIPO did not join the appeal, the newspaper said, and a spokeswoman for the agency refused to comment when telephoned.

The Chinese drug companies are challenging New York-based Pfizer's exclusive right to Viagra by seeking to make sildenafil citrate, the main active ingredient in the pill.

"We must try our best to protect our interests," Wang Wei, a lawyer representing the dozen companies was quoted as saying by the China Daily.

The companies are based all over China, from the northeastern province of Jilin to Guangdong in the south. They claim they have invested 100 million yuan ($12 million) to make less expensive imitations, the newspaper said, without giving more details.

China is a potentially huge market for Viagra, which was introduced in the country in 2000. Known locally as "weige," or "great brother" in Chinese, it gained a huge following given the country's tradition of using various substances to boost sexual performance.

As a part of its WTO commitments, China has agreed to tighten protections on patents, copyrights and trademarks and said it would encourage its own companies to invest in creating profitable new drugs and other products.

Yet despite repeated pledges to crack down on the rampant counterfeiting, pirated goods from branded clothes to movies to toys are still readily found on almost any street corner.

Most drugs with the "Viagra" label sold in China are bogus versions. Six months after Viagra was introduced, state media reported that some 90 percent of little blue pills sold in Shanghai were fake.

--The Associated Press