High-performance liquid chromatographic assay of pyrimethamine, sulfadoxine and its N4-acetyl metabolite in serum and urine after ingestion of Suldox.

A sensitive and selective reversed-phase high-performance liquid chromatographic assay has been developed to determine the concentration of pyrimethamine, sulfadoxine and N4-acetylsulfadoxine in serum and urine after oral administration of the antimalarial remedy Suldox. Hitherto the literature describes no method being able to quantitate all three compounds in these fluids. The compounds are extracted successively from the same sample and subjected to liquid chromatography followed by ultraviolet detection (280 nm). Calibration curves were linear (r2 = 0.999; S.E.M. less than 3%; n = 10) in the range 0-300 micrograms/ml (sulfadoxine) and 0-1000 ng/ml (N4-acetylsulfadoxine and pyrimethamine). The limits of quantitation for the latter compounds were as low as about 5 ng/ml and 1 ng/ml, respectively. At therapeutic serum concentrations of 30 micrograms/ml (sulfadoxine), 350 ng/ml (N4-acetylsulfadoxine) and 120 ng/ml (pyrimethamine) an interassay reproducibility below 8% (relative standard deviation) was found for all three compounds. The assay was evaluated in a pilot study and proved convenient for pharmacokinetic studies in man following oral co-administration of pyrimethamine and sulfadoxine.