[Malaria and drug resistance]

Drug resistance is a major problem in malaria. The resistance mechanism remains unresolved but contributing factors are probably heavy drug use, parasite selection, cross resistance and genetic influences of drugs. Plasmodium ovale en P. malariae are sensitive to the current antimalarial drugs. P. vivax has some chloroquine resistant strains, notably on Papua New Guinea, Irian Jaya and other islands in the Pacific. The geographical distribution of P. falciparum strains resistant to proguanil and pyrimethamine is not well known. Chloroquine-resistant strains are found in South East Asia, the Amazon region (almost 100% resistance in both regions) and in Africa south of the Sahara (resistance not everywhere 100%). Sulfadoxine-pyrimethamine is not an effective treatment in South East Asia and the Amazon region; it is useful in tropical Africa. Mefloquine resistance is a problem mainly confined to Thailand. There is cross resistance between halofantrine and mefloquine. Decreased sensitivity to quinine was reported from Thailand, but it remains an effective drug, notably when given in combination with tetracycline or doxycycline. In cases of severe or complicated malaria intravenous quinine is still the preferred therapy. Resistance to artemisinine has not yet been reported. Pharmaceutical companies show little interest in antimalarial drug development, which in view of the increasing drug resistance is a matter of great concern.