Sensitivity to artemisinin, mefloquine and quinine of Plasmodium falciparum in northwestern Thailand

The increasing drug resistance of Plasmodium falciparum is a worldwide problem. The objective of the study was the assessment of the in vitro activity of artemisinin, mefloquine and quinine, in an area where P. falciparum is multi-drug resistant. The sensitivity tests were based on measuring the drug-dependent inhibition of schizont maturation. For the 43 successfully tested isolates the mean effective concentrations (IC50 and IC90) for artemisinin were 0.0081 and 0.1372 mu M, respectively. For mefloquine the IC50 was 0.1260 mu M and the IC90 was 3.7345 mu M. Quinine showed an IC50 of 0.2155 mu M and an IC90 of 2.5040 mu M. All tested drugs showed a significant reduction in the effectiveness, compared with the results of former years. This suggests a further rise of resistance of local P. falciparum, which is alarming especially for artemisinin and quinine.