Chinese generic drug makers are now preparing for a possible big payday when the patent on Pfizer's blockbuster drug Viagra expires in China next July.

While good news for patients seeking cheaper alternatives and companies making generic versions, it means a serious financial hit for Pfizer, according to a report in the Securities Times.

China had a potential market of more than 20 billion yuan ($3.25 billion) for drugs treating erectile dysfunction in 2012. Viagra sales accounted for about 5 percent of the total market.