Determination of theophylline in serum and saliva in the presence of caffeine and its metabolites.

Because of marked variability in its metabolic clearance and its narrow therapeutic range (10-20 micrograms/ml) investigation of each patient's clearance of theophylline is desirable. The author reports here a rapid reversed-phase high-performance liquid chromatographic (HPLC) method to determine, within 3 min, the theophylline in serum and saliva in the 0.1-50 micrograms/ml range. A fast HPLC column, 10 x 4.6 mm, packed with 3-microns spherical ODS packing is used with acetonitrile-methanol-buffer pH 4.7 (4:7:89) to achieve separation of theophylline from paraxanthine and matrix components. Since theophylline is a major pediatric bronchodilator, the feasibility of assay in saliva was investigated as an alternative route for determining the clearance is stressed asthmatic children. Using this method it was found that the ratio of theophylline in simultaneous serum and saliva samples is very consistent over time in the same person (+/- 3.99%), but inter-individually this consistency is reduced ten-fold. Simultaneous serum and saliva samples need be taken only once to obtain the ratio and the kinetics followed further with salivary samples only.