Antimalarial Drug Susceptibility of Plasmodium vivax in the Republic of Korea

The antimalarial susceptibility of ring stage (> 80%) Plasmodium vivax from the Republic of Korea, where long incubation-period strains are prevalent, was evaluated using the schizont maturation inhibition technique. During 2005-2007, susceptibility to seven antimalarial drugs was evaluated with 24 fresh isolates. The geometric mean (95% confidence interval) 50% inhibition concentration (IC(50)) were quinine 60 (54-75) ng/mL, chloroquine 39 (22-282) ng/mL, piperaquine 27 (17-58) ng/mL, mefloquine 39 (35-67) ng/mL, pyrimethamine 138 (89-280) ng/mL, artesunate 0.6 (0.5-0.8) ng/mL, and primaquine 122 (98-232) ng/mL. Positive correlations were found between quinine and mefloquine (r = 0.6, P = 0.004), piperaquine and chloroquine (r = 0.6, P = 0.008), and piperaquine and primaquine IC(50) values (r = 0.5, P = 0.01). Compared with P. vivax in Thailand, P. vivax in the Republic of Korea was more sensitive to quinine and mefloquine, but equally sensitive to chloroquine and artesunate.