In a new report published today, ''Susceptibility of Plasmodium Falciparum to Antimalarial Drugs,'' the World Health Organization (WHO) warns that as more and more people gain access to these life-saving malaria medicines, which combine a drug derived from the plant Artemisia annua with a second, synthetic drug, it is vital that countries closely monitor their effectiveness.
More than 50 governments have followed WHO's recommendations on malaria treatment and adopted artemisinin-based combination therapies (ACTs), the most effective antimalarial drugs available today. This has enhanced prospects for reducing the burden of the disease worldwide.
Drugs derived from the plant Artemisia annua must be used as ACTs in combination with a second drug, and not alone. Otherwise, the medicines could lose their potency over time due to the development of resistance. This has already happened with other antimalarial drugs in the past. ''It is crucial that these medicines be used correctly,'' said Dr Pascal Ringwald, a medical officer in WHO's Roll Back Malaria (RBM) Department and principal author of the new report on global monitoring of antimalarial drugs.
To avert resistance, WHO is calling on countries to use only WHO-approved ACTs (an artemisinin-based drug combined with amodiaquine, lumefantrine, mefloquine or sulfadoxine-pyrimethamine) of high quality, since drugs of low potency can promote resistance. The organization also advises that all people taking antimalarials should be educated about the importance of finishing their medication courses, since incomplete treatment is another cause of resistance. Any change in efficacy of antimalarial drugs should prompt an appropriate update in a country's treatment policy.
The danger of resistance stems from the malaria parasite's ability to evade the lethal action of drugs. Because malaria parasites are genetically highly diverse, some strains can escape drugs unharmed and pass along their resistance to progeny. As sensitive organisms die off, resistant strains may come to dominate, and over time an antimalarial drug can lose its ability to cure infection.
Resistance is more likely to occur when only one drug is used. Combining an artemisinin-based medicine with another antimalarial drug, as WHO recommends, sharply reduces the risk. ''To date no treatment failures due to artemisinin drug resistance have been documented, but we are watching the situation very attentively,'' Dr Ringwald said.
The report recounts the emergence of resistance to the former mainstays of malaria treatment, such as chloroquine, in most regions of the world, and the ways countries have changed their national policies to keep ahead of the advancing resistance. It also outlines new standardized methods developed by WHO for monitoring antimalarial drug efficacy and emerging resistance patterns worldwide.
''We have the means to enhance the lifespan of ACTs. In addition, we must move forward energetically on research to develop new antimalarial medicines,'' said Dr Fatoumata Nafo-Traore, Director of WHO's RBM Department.