IN-VITRO SUSCEPTIBILITY STUDIES OF PLASMODIUM-FALCIPARUM ISOLATES ANDCLONES AGAINST TYPE-II ANTIFOLATE DRUGS

Six clones were derived from each Plasmodium falciparum isolate obtain ed from Malaysia, Africa and Thailand and were characterized against t ype II antifolate drugs, cycloguanil and pyrimethamine using the modif ied in vitro microtechnique. Results showed that these isolates were o f a heterogeneous population, with 50% inhibitory concentrations of Go mbak A clones at 0.0151-0.1450 and 0.0068-0.1158 mu M, Gambian clones at 0.0056-0.1792 and 0.0004-0.0068 mu M and TGR clones at 0.0103-0.070 3 and 0.0776-0.3205 mu M against cycloguanil and pyrimethamine, respec tively. All clones displayed similar susceptibilities as their parent isolates except A/D3, A/D5, A/G4 and A/H7 clones which were sensitive to cycloguanil at 0.0735, 0.0151, 0.0540 and 0.0254 mu M but Gm/B2 clo ne was resistant at 0.1797 mu M, respectively. However, A/D3, TGR/B4, TGR/B7, TGR/C4, TGR/C7 and TGR/H2 clones were resistant to pyrimethami ne at 0.1158, 0.1070, 0.1632, 0.1580, 0.2409 and 0.3205 mu M respectiv ely. Further results indicated that they were pure clones compared to their parent isolates as their drug susceptibility studies were statis tically different (p < 0.05).