Volume 34, Issue 2
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Antimalarial activity of chloroquine, quinine, mefloquine and halofantrine against 33 strains of isolated from naturally acquired malaria infections in Thailand was determined using a radioisotope microdilution method. A microtitration procedure was used to test isolates of against the 4 drugs simultaneously. The mean ID for chloroquine and quinine reflected known resistance to those drugs in Thailand. The mean ID for mefloquine and halofantrine showed susceptibility to these drugs. Four isolates of however had markedly decreased susceptibility to melfloquine (ID > 15 ng/ml); one case of which was confirmed as the first case of RII resistance for mefloquine in Thailand. Several parasite isolates were also observed to have decreased susceptibility to the new drug, halofantrine. These studies strongly recommend that in vitro testing be done in conjunction with field evaluation of new antimalarial drugs.


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