Plasmodium: resistance to antimalarial drugs.

Quinine-resistant Plasmodium falciparum was first reported in 1910 from Brazil. Today this parasite is resistant in most endemic areas to the widely used blood schizonticide, chloroquine. Many strains are resistant also to antifols (e.g. pyrimethamine, proguanil) and some are also no longer eliminated by quinine. These polyresistant parasites have an enhanced ability to resist also new drugs such as mefloquine and halofantrine. There are indications that P. vivax is also becoming resistant to chloroquine in Papua-New Guinea where primaquine resistance of the hypnozoites also exists. The modes of action of antimalarials and mechanisms by which parasites become resistant to them are discussed. Future developments include the search for radically new compounds, for drugs that reverse chloroquine resistance and for new strategies to impede the progress of this problem.