High performance liquid chromatography (HPLC) has indicated possible evidence that resistance to artesunate is developing in the Thai-Myanmar border regions.
The drug is used in combination with mefloquine to tackle symptomatic acute uncomplicated Plasmodium falciparum malaria.
In the study, published in Malaria Journal, 150 patients - including 65 females and 85 males - were examined after seven and 42 days.
HPLC was used to detect mefloquine levels in the blood, while
liquid chromatography-mass spectrometry was applied to the analysis of concentrations of plasma artesunate and its metabolite dihydroartemisinin.
The scientists note that some ethnicity effects mean that resistance to melfoquine already exists in P falciparum.
But they add that their findings carry support for the suggestion that resistance to artesunate is also developing.
Malaria Journal is edited by Marcel Hommel at the University of Liverpool, while the scientists are from Thammasat University in Thailand and Mae-Sot General Hospital in Thailand's Tak province.