The 2015 Nobel in medicine went to persons who discovered certain new antibiotic agents, among them Dr. Satoshi Ōmura and Dr. William Campbell, who discovered ivermectin. Ivermectin is used in Africa for parasitic infections, but in this country it's used in veterinary medicine, mostly in horticulture and in ranching as a cattle de-worming agent, and is not licensed for people. Why? Probably not profitable due to parasitic infections being rare in the USA overall these days, and given the high cost for studies needed to approve a drug with the FDA.
Personally, I think there should be a third FDA approval pathway that allows meds fully off patent to be licensed without a full approval process, but only as fully generic (anyone may make and sell if they make a product of adequate purity and bio-availability). Instead, what we have in this country is the Orphan Drug Act, which has been misused so as to become a prime example of the abuse of US law by corporations' greed.
