Development and clinical application of high performance liquid chromatography for the simultaneous determination of plasma levels of theophylline and its metabolites without interference from caffeine

A high performance liquid chromatography (HPLC) method has been developed f or the simultaneous determination of plasma levels of theophylline and its metabolites without interference from caffeine or caffeine metabolites. The method is simple and of practical use because it is applicable even to pla sma samples from patients who take caffeine-containing beverages. The metho d was also reproducible with a coefficient of variation of less than 5% for each analyte. The levels of theophylline, determined by HPLC, were validat ed by their high correlation to the levels obtained by fluorescence polariz ation immunoassay. HPLC was used to determine theophylline levels in patien ts with bronchial asthma. The data revealed that the ratio of 1,3-dimethylu ric acid, the major metabolite of theophylline, to theophylline concentrati on in the plasma was within a narrow range in most patients (0.055 +/- 0.01 , n = 66), regardless of the method of theophylline administration or the t ime of blood sampling. Conversely, this ratio was as low as 0.027 +/- 0.005 in the patient with a long plasma half-life of theophylline. These results suggest that it may be possible to predict the plasma half-life of theophy lline for each patient from a single blood sample. This may be useful when planning theophylline administration, especially in patients with abnormal theophylline metabolism. Copyright (C) 1999 John Wiley & Sons, Ltd.