Reliability of salivary theophylline as a guide to plasma theophylline levels

S. P. Galant, S. A. Gillman, L. H. Cummins, P. P. Kozak and J. J. Orcutt

Simultaneous saliva and plasma theophylline levels in 12 chronic asthmatic children were measured by high pressure liquid chromatography following administration of a theophylline preparation. In five subjects, simultaneous plasma and salivary theophylline were measured one week later. A strongly positive correlation between plasma and salivary theophylline levels was found at all time periods tested. There was no substantial difference in the plasma-saliva theophylline ratio determined one week later. A predicted plasma level was compared with the observed value. The proportionality of predicted to observed plasma theophylline levels using either the entire study group mean plasma-saliva ratio or each individual's ratio was approximately 1.00 with 9% variability. When a previously reported plasma-saliva theophylline ratio was used for comparison, the predicted plasma theophylline was 15% above the observed plasma level.