Simultaneous determination of pyrimethamine and sulphadoxine in human plasma by high-performance liquid chromatography after automated liquid-solid extraction

Abstract A high-performance liquid chromatographic method with ultraviolet detection is described for the simultaneous measurement of pyrimethamine and sulphadoxine in human plasma. After an automated liquid-solid extraction on a C 8 cartridge, the compounds are separated on a C 18 column by isocratic elution; the mobile phase is methanol-acetonitrile-water (10:25:65, v/v/v) with triethylamine (1%) and adjusted to pH 5.6 with phosphoric acid. The eluent is monitored with an ultraviolet detector at 240 nm. The limit of quantification was 10 ng/ml for pyrimethamine and 22 μg/ml for sulphadoxine. No chromatographic interferences can be detected from endogenous compounds, other anti-malarial drugs or major drugs used for the treatment of children. Sulphadimethoxine is used as an internal standard. The method is accurate and precision is good with relative standard deviations lower than 6%. The chromatographic procedure takes 11 min. The method is comparatively rapid, simple, sensitive and can be used for therapeutic drug monitoring, clinical and pharmacokinetic studies.