Malaria resistance could lie at counterfeits' door

Researchers in southeast Asia who found further evidence of a rise in malarial parasites showing resistance to artemisinin-based treatments, which might be attributable to exposure to counterfeit medicines, have now published their findings in the New England Journal of Medicine.

The team, from the Mahidol Oxford Research Unit in Bangkok, compared the efficacies of artesunate-based treatments for uncomplicated malaria caused by Plasmodium falciparum in Pailin, western Cambodia, and Wang Pha, northwestern Thailand.

Among patients who were treated with artesunate as a monotherapy, those in Cambodia took almost twice as long to clear the parasite from their bodies, and a resurgence of the parasite, measured using DNA testing, occurred in 30 per cent of the Cambodian patients and just 10 per cent of those in Thailand.

Among patients receiving a combination regimen of artesunate and mefloquine, resurgence was around 5 per cent in both Cambodia and Thailand. Crucially, the differences could not be explained by pharmacokinetic or other patient factors.

“A few cases of reduced efficacy of artemisinin-based combination therapy have been reported previously,” the authors write. “Most of these cases can be explained by the counterfeit nature of the drugs tested.”

Southeast Asia has traditionally been the area where resistance to earlier generations of antimalarial drugs – such as chloroquine and sulfadoxine-pyrimethamine – was first encountered (see also Malaria crisis looming: are fake drugs to blame?)

“Measures for containment are now urgently needed to limit the spread of these parasites from western Cambodia and to prevent a major threat to current plans for eliminating malaria,” say the authors.

For a limited period the full text of the article will be available on the NEJM’s website.