A Model in Vitro System to Test the Susceptibility of Human Malarial Parasites to Antimalarial Drugs

Abstract

The rocker dilution technique was adapted for in vitro testing of antimalarial drugs on five strains of Plasmodium falciparum. Seven antimalarial drugs, chloroquine (concentrations: 0.0075, 0.015, 0.03, 0.06, 0.12, 0.3, 0.6, 1.2 µg/ml culture), amodiaquine (0.12 and 0.3 µg/ml), pyrimethamine (3.6 and 5.5 µg/ml), quinine (2.5 and 5.0 µg/ml), cycloguanil (0.144 µg/ml), trimethoprim (50.0 µg/ml) and dapsone (2.5 µg/ml) were tested. The various strains of P. falciparum were classified as susceptible or resistant to a drug depending upon the concentration of agent required to: a) inhibit maturation of rings to trophozoites (i.e., prevent cytoplasmic growth); b) block formation of schizonts and segmenters (i.e., prevent nuclear multiplication); or c) produce aberrant distribution of chromatin within the parasite. A strain of P. falciparum obtained from Arnold and Martin is resistant to pyrimethamine and quinine, but susceptible to chloroquine. The Malayan-Camp. strain is susceptible to chloroquine. The Vietnam-Oak Knoll strain is resistant to chloroquine. Two strains (the Uganda-Palo Alto and the Vietnam-Monterey) were studied in greater detail. Of the five strains studied, the Uganda-Palo Alto strain proved to be the most susceptible and the Vietnam-Monterey strain the most resistant to chloroquine. Both of these strains are susceptible to amodiaquine, cycloguanil and dapsone. The Uganda-Palo Alto strain is resistant to trimethoprim and pyrimethamine, while the Vietnam-Monterey strain is susceptible to these two drugs.