Simultaneous and Specific Determination of Proxyphylline, Theophylline and other Xanthine Derivatives in Serum by High Pressure Liquid Chromatography

A HPLC‐method for rapid, simultaneous and specific determination of proxyphylline, theophylline, glyphylline, theobromine, caffeine and 3‐methylxanthine using 8‐chlorotheophylline as internal standard is presented. Using 20 μl deproteinised serum samples for injection, the detection limits for theophylline and proxyphylline are about 0.040 and 0.055 μg per ml serum or plasma, respectively, and the corresponding sensitivities are about 0.033 and 0.048 μg compound for 0.0044 absorbance units at 280 nm. In duplicate analyses the coefficient of variation is less than 3%. A number of frequently used drugs did not interfere in the analyses of serum samples from patients under treatment or in experiments with drug additions to serum samples.