Malaria
Chloroquine kills the Plasmodium in the blood. But the Plasmodium in the liver is not killed by chloroquine. P. vivax and P. ovale both stay in the liver a long time. This is the dormant phase. Another medicine must be given with chloroquine for P. vivax and P. ovale. This is to kill the Plasmodium in the liver. The medicine used to kill malaria in the liver is primaquine. In southeast Asia, some P. vivax is resistant to primaquine. Most other places, primaquine works very well.