Pfizer's ($PFE) patent for erectile dysfunction drug Viagra goes off patent in China next month and drugmakers are lining up to produce cheap versions of the little blue pill. "We are not sure whether our ED drug will generate much profit, but we know it is a huge market," Chen Jing of Chinese drugmaker Guangzhou Baiyunshan Pharmaceutical told Shanghai Securities News. Pfizer reported 2013 sales of $1.9 billion for Viagra, down 8%. It reported reported international sales of the drugs were down 18% as its Viagra patents in many European countries expired last year. It has a deal in the U.S. for Teva Pharmaceutical Industries ($TEVA) to produce a generic beginning in 2017. Story | More