Big Pharm gets exclusive 'rights' to the drug and can ask any amount of money for it. I found this out a few years ago when I needed to by XALATAN to fight my dog's glaucoma. Costs pennies to make, was developed with public money. A tiny bottle which lasted us for only 19 days cost over $89 in the USA. I imported it from Canada for less than half.
http://www.cptech.org/ip/health/econ/govrnd.html"The Chinoin-Pharmacia partnership has been a profitable one. Chinoin is making a 50 percent return on its prostaglandin investment, company officials said. And Pharmacia pays Chinoin slightly more than $5 million a year for the manufacturing of latanaprost, said Tibor Szabo, who directs the prostaglandin business unit at Chinoin.
That amounts to roughly one one-hundredth of Xalatan's $507 million in annual sales last year. Or, to put it another way, the cost of making the key ingredient is just 1 percent of the revenue Xalatan generates."