The effect of artemisinin combined with standard antimalarials against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum in vitro.

The activity of artemisinin (qinghaosu) in combination with some commonly-used antimalarial drugs was tested in vitro against a chloroquine-sensitive (NF54) and a chloroquine-resistant (K1) strain of Plasmodium falciparum. Both mefloquine and tetracycline showed marked potentiative synergism with artemisinin against both strains, whilst primaquine showed potentiation against K1. Combinations of artemisinin with pyrimethamine and with chloroquine were antagonistic. The results confirm observations on rodent malaria in vivo and indicate that the drug interactions seen were direct, through actions on the parasite, and not merely effects on drug distribution and metabolism in the mouse host.