Abstract
Background: Exposure of Plasmodium falciparum to increasing sublethal drug concentrations followed by drug treatment led to the development of many resistant parasites. Therefore, the susceptibility of these clones to the type II antifolate drugs, cycloguanil and pyrimethamine, before and after subculturing them in vitro for a period of 3 years, was studied. Methods: Thirty fresh clones were obtained from five different blood samples infected with P. falciparum isolates. They were tested for their susceptibility to the above drugs during the investigation period. Results: None of these clones changed their susceptibilities, before and after the investigation period. Conclusion: This study gives further evidence that there is no alteration of the susceptibilities of the clones to the above drugs during the investigation period.