A reversed-phase high-performance liquid chromatographic method using a mobile phase of
acetonitrile-
methanol-
trifluoroacetic acid-water (16.1:7.2:0.1:76.6, v/v/v/v) at a flow rate of 1.0 ml min(-1) on a LiChrospher RP-18 column with UV (254 nm) detection has been developed for the separation of
sulfadoxine and its metabolite N-acetyl
sulfadoxine in plasma. No interferences due to endogenous compounds or common
antimalarial drugs were noticed. The limit of detection for
sulfadoxine and N-acetyl
sulfadoxine was 0.01 microg ml(-1) with a signal-to-noise ratio of 5:1 while the limit of quantification was 2.5 microg ml(-1). Intra-day mean relative standard deviations (RSD's) for
sulfadoxine and N-acetyl
sulfadoxine were 2.6 and 2.8%, respectively, while mean inter-day RSD's for
sulfadoxine and N-acetyl
sulfadoxine were 2.4 and 2.8%, respectively. Extraction recoveries averaged 90.6% for
sulfadoxine and 86.9% for N-acetyl
sulfadoxine. The method was applied for the assay of
sulfadoxine and its metabolite N-acetyl
sulfadoxine in plasma from
Plasmodium falciparum malaria patients. Mean plasma
sulfadoxine concentrations on day 2 (51 h) from samples collected from sensitive and resistant P. falciparum patients treated with three
tablets of
Fansidar were 62.8 and 60.5 microg ml(-1), respectively. Mean ratio of N-acetyl
sulfadoxine to
sulfadoxine was 9.1% for responders and 13.9% for non-responders which revealed that higher amounts of the metabolite N-acetyl
sulfadoxine were present in non-responders. The method described should find an application in the therapeutic monitoring of
malaria patients.