Non-extraction HPLC method for the simultaneous measurement of theophylline and caffeine in human serum

A non extraction HPLC method is described for the simultaneous measurement of theophylline and caffeine in human serum using a Pinkerton ISRP column and u.v. detection at 275 nm. The method is suitable for therapeutic monitoring of theophylline levels in adults and, in particular, quantitation of both theophylline and caffeine in premature neonates where as little as 10 microL of sample can be used. Comparison of theophylline levels obtained by this method with EMIT analysis show a correlation coefficient of 0.97 (n = 37) in adults and 0.79 (n = 16) in premature neonates. There was no correlation between serum theophylline and caffeine levels in premature neonates receiving theophylline therapy. No interference was encountered from endogenous plasma components or other drugs in the 53 patients studied. Precision of the assays compares well with reported values for extraction HPLC and immunochemical analyses.