In 1953, a new drug was released by Burroughs Wellcome, a pharmaceutical company based in London. Pyrimethamine, as the compound was named, was originally intended to fight malaria, after the microorganisms that cause the disease developed resistance to earlier therapies. The drug was used against malaria for several decades, often in combination with other compounds. It’s mostly used now to treat toxoplasmosis, a parasitic infection that can be life-threatening in people whose immune systems are suppressed, for example, by HIV/AIDS or cancer.
More than 40 years later, Burroughs Wellcome merged with the British pharmaceutical giant Glaxo. In 2010, the company, now GlaxoSmithKline,sold the U.S. rights to pyrimethamine — which is marketed under the brand name Daraprim — to another firm, CorePharma. By then, the patent on the drug had long since expired, but because nobody bothered to make a generic, Daraprim was essentially a monopoly.
– The Washington Post