Food and pharmaceutical company CJ CheilJedang on Wednesday filed a nullity suit against Pfizer over the “use” patent of impotence medicine Viagra.

“This is the first lawsuit filed to nullify the patent of Viagra in Korea. Other drug companies that are preparing for the generic forms are also keeping a very close watch on it,” a CJ official said.

U.S.-based drug maker Pfizer holds two patents for Viagra, one for the chemical itself, expiring in 2012, and the other for its use against impotence, expiring in 2014 here.

If the court upheld CJ’s claim, local drug makers would be allowed to start to market a generic version of the “little blue pill” from May 17 next year. 

CJ is one of 16 companies that have embarked on the development of generic Viagra. The company said it has completed the bioequivalence tests and plans to apply for the approval from the Food and Drug Administration.

Citing cases in the United States, however, Pfizer Korea expected that it would keep the 2014 patent protection.

“The use patent of Viagra has been maintained not just in Korea but also in countries such as the United States, Japan, China and Australia. We hope the court will reconfirm the validity of our patent,” a Pfizer Korea official said in an interview.

In August, Pfizer won in a patent-infringement case against Teva Pharmaceutical Industries, the biggest generic-drug company.

Depending on the court ruling, CJ could pay a lot of money in compensation to Pfizer. The company said it would finalize the release date of its generic medicine following the court decision.

According to industry data, Korean sales of erectile dysfunction drugs amount to 100 billion won ($86 million) per year, of them Viagra makes up 40 billion won.

By Lee Ji-yoon (jylee@heraldcorp.com)