Host failure in treatment of malaria with sulfalene and pyrimethamine

Determination of sulfalene in plasma, red blood cells and whole blood by high-performance liquid chromatography

A normal phase high-performance liquid chromatographic method using dichloromethane-methanol-perchloric acid (1 M) (96:9:1, v/v) at a flow-rate of 1 ml/min on a Nucleosil 100-7 column (250 x 8 x 4 mm) and UV detection at 254 nm, has been developed to determine the concentration of sulfalene in plasma, red blood cells and whole blood after oral administration of the antimalarial drug metakelfin. The coefficient of variation was 7.1% and the extraction recovery was 82%. Mean concentrations of sulfalene on days 1, 7 and 15 were: 49.56, 10.46 and 2.24 micrograms/ml in plasma, 25.02, 4.34 and 0.84 micrograms/ml in red blood cells and 21.12, 4.44 and 1.00 micrograms/ml in whole blood, respectively. Quinine, chloroquine, desethylchloroquine, mefloquine, primaquine, sulfadoxine, pyrimethamine and dapsone did not interfere in the detection of sulfalene.

The dynamics of drug resistance in Plasmodium falciparum

Drug resistance of Plasmodium falciparum is not a recent phenomenon, but it became a major problem when the parasite became resistant to chloroquine, the cheapest and initially the most effective antimalarial compound that could be used for treatment and suppression. In some areas this problem is compounded by resistance to the first line of alternative drugs, and rapid loss of sensitivity to the next line. The dynamics of drug resistance are regulated mainly by drug related selection pressure and intensity of malaria transmission. Mass drug administration in its various forms, and insufficient treatment are obviously the most important motors of selection.

In vitro activities of and mechanisms of resistance to antifol antimalarial drugs

Certain drugs that interfere with folate metabolism (sulfones, sulfonamides, and inhibitors of dihydrofolate reductase) play an important role in the chemotherapy and prophylaxis of malaria. The activities and mechanisms of action of these drugs are regarded as similar in most respects to their activities against procaryotic microorganisms. Believed incapable of utilizing intact exogenous folates, plasmodia have been regarded as dependent on de novo synthesis of required folate cofactors. The present investigation, conducted in pursuit of a method for testing the in vitro susceptibility of Plasmodium falciparum to antifol antimalarial drugs, produced evidence that earlier assumptions about the folate metabolism of this organism are not correct. Three of four isolates of P. falciparum were successfully maintained in a culture medium depleted of folic acid and p-aminobenzoic acid. The antimalarial activities of sulfonamides and dihydrofolate reductase inhibitors were, furthermore, variably antagonized by the presence of folic acid and p-aminobenzoic acid in the culture medium. Optimum conditions for assessment of antifol antimalarial activity in vitro therefore require precise control of these factors in the culture medium. Our results suggest that resistance to antifol antimalarial drugs involves a complex of factors related to both the de novo synthesis of active folate cofactors and the ability to utilize exogenous intact folates in various forms.

Comparison of in vitro pyrimethamine assays and in vivo response to sulphadoxine-pyrimethamine in Plasmodium falciparum from Papua New Guinea

The in vitro pyrimethamine sensitivity of 20 Plasmodium falciparum isolates from Papua New Guinea children was determined. The children were treated with sulphadoxine-pyrimethamine and six were found to have clinically resistant malaria. The P. falciparum isolated from these subjects were more resistant to pyrimethamine in vitro than 13 of the isolates from sensitive cases. These results suggest that pyrimethamine sensitivity alone may be a good indicator of in vitro response to sulphadoxine-pyrimethamine.

Haemolytic effect of two sulphonamides evaluated by a new method

A technique to investigate drugs which could cause haemolysis in subjects deficient in glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP oxidoreductase; G6PD) has been developed. The method is based on the technique of 14CO2 evolution during the incubation of normal erythrocytes in the presence of [I-14C]glucose and their own serum, the latter containing the active metabolites of the drugs received by normal subjects. By this method agents causing a stimulation of the hexosemonophosphate pathway of normal erythrocytes should be regarded as potentially haemolytic for G6PD-deficient subjects. Two sulphonamides, sulphormethoxine and sulphalene, of which until now no haemolytic effects have been reported, together with chloroquine, have been investigated. While chloroquine does not affect the hexosemonophosphate shunt of normal erythrocytes, the two sulphonamides stimulate this pathway. THE RESULTS ARE CONFIrmed by the reduction of the half-life of 51Cr-labelled G6PD-deficient red cells (Mediterranean variant), after administration of the two sulphonamides.