Determination of sulfadoxine in human blood plasma using packed-column supercritical fluid chromatography

A sensitive, rapid, selective and reproducible method has been developed to measure plasma levels of sulfadoxine, 4-Amino-N-(5, 6-dimethoxy-4-pyrimidinyl) benzensulfonamide; in healthy, human volunteers using packed-column supercritical fluid chromatography. Omeprazole, 5-methoxy-2-[[(4-methoxy-3, 5-di-methyl-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole; was used as the internal standard (i.s.) at 15.0 μg/ml. The drug and the i.s. were extracted from plasma using dichloromethane. Separation of sulfadoxine and i.s. was done on a Nucleosil (250×4.6 mm) 10 μm, RP-C18 column with 7.4% (v/v) methanol-modified supercritical fluid carbon dioxide (2.5 ml/min) as the mobile phase. The column temperature was 40°C and the outlet pressure was set at 8.83 MPa. The detection was done using a UV–Vis detector set at 265 nm. The limit of quantification was 0.50 μg/ml using 1 ml plasma specimen. The mean extraction recovery of the drug from plasma was found to be 94.9%. The SFC method was directly compared to a published HPLC/UV method. With respect to speed and use of organic solvents SFC was found to be superior; while in all other aspects the results were similar to the published technique. The method has been successfully used to estimate the sulfadoxine levels in healthy human volunteers from 0 to 240 h following an oral dose of 500 mg of sulfadoxine in combination with 25 mg of pyrimethamine.