Simultaneous analysis of theophylline, caffeine and eight of their metabolic products in human plasma by gradient high-performance liquid chromatography.

A method has been developed for the simultaneous determination of methylxanthines and many of their metabolites in plasma. Specially developed extraction columns (Celute-MX) were used and the extracts were separated on a 25-cm ODS column (particle size, 3 microns) at 50 degrees C with a mobile phase gradient. The compounds were detected with a diode array detector at two analytical wavelengths. The value of drug metabolite ratios has been explored and elevated ratios have been found when metabolic clearance was impaired by disease or co-administered drugs. Large concentrations of pharmacologically active metabolites have been found in renal failure. The assay has proved to be reliable and valuable in the elucidation of therapeutic and metabolic problems involving the methylxanthines.