Comparative pharmacokinetic analysis of theophylline in serum and saliva

The kinetics of theophylline disposition in serum and saliva was evaluated after single and multiple circadian administration of a sustained-release theophylline formulation (Euphyllin CR) to 20 asthmatic children. Salivary concentrations were proportional to serum drug levels, with the significant correlation of r = 0.92. The kinetics of theophylline absorption and elimination and the mean residence time were identical in both saliva and serum estimations. In steady-state conditions after multiple drug administration, the area under the concentration-time curve and the magnitude of peak levels in saliva were reduced proportionally with decreased serum theophylline concentrations. The significantly higher volume of theophylline distribution in saliva confirmed that salivary concentrations represent the free, pharmacologically active fraction in plasma. The determination of theophylline salivary levels could therefore be of clinical importance. The values of the saliva/serum ratio determined in the elimination phase of concentration-time curves for individual patients were constant and stable over the treatment period of three weeks. Saliva appears to be a convenient and noninvasive alternative to blood for the assessment of the variable pharmacokinetic parameters of theophylline and for around-the-clock monitoring of individual dosage regimens, especially in paediatric patients.