In vitro sensitivity of Plasmodium falciparum to lumefantrine in north-western Thailand.

Lumefantrine (benflumetol) belongs to the class-2 blood schizontocidal compounds. In combination with artemether it serves as an alternative drug for treating chloroquine-resistant infections with Plasmodium falciparum. In view of activity correlations with mefloquine, it is important to monitor the parasite's intrinsic sensitivity to lumefantrine in areas with multi-drug resistant P. falciparum, the objective of this study. The observations were carried out in 2002 at Mae Sot, northwestern Thailand, near the border to Myanmar. The 41 successfully in-vitro tested parasite isolates yielded a geometric mean cut-off concentration of schizont maturation of 237.54 nM, and EC50, EC90 and EC90 values of 15.13 nM, 86.71 nM and 359.97 nM, respectively. As compared to the findings of 1998 and 1999, the susceptibility to lumefantrine has increased, possibly due to the improved therapeutic response of mefloquine-resistant P. falciparum infections to combined treatment with artesunate + mefloquine. The EC9o and EC99 data of 2002 for lumefantrine in the study area suggest fully curative clinical-parasitological efficacy.