more research—and that early wins such as arsphenamine were more than just isolated flukes. This was a time period when organic chemistry's largest economic applications included textile dyes, explosives, munitions, and chemical weapons but not yet pharmaceuticals. The fact that systematic, iterative experiments had eventually synthesized an antimalarial drug that was 30 times more effective than quinine while being safe enough to use (relative to the bleak alternatives of the era) supported the concept of modern pharmaceutical research laboratories as it would develop in coming decades. A large trial of pamaquine performed by the Royal Army Medical Corps and the British Indian Medical Service in 1929 showed for the first time that it was possible to prevent relapse of vivax malaria. Prior to this, it was understood that patients with vivax malaria would suffer from relapses, but there was no treatment that could prevent the relapses from occurring. The relative weights of treatment benefit and harm change over decades as science advances. About a decade after pamaquine became available, chloroquine arrived, and about a decade after that, primaquine arrived. Pamaquine is more toxic and less efficacious than primaquine; therefore, pamaquine is no longer routinely used, and of the two, only primaquine is currently recommended by the World Health Organization. References Antimalarial agents Quinolines Phenol ethers Diethylamino compounds