Study of bioavailability and pharmacokinetics of theophylline following administration of two sustained release dosage forms as assessed by salivary data: Part II.

Bioavailability and pharmacokinetics of theophylline following administration of a marketed sustained release tablet (Theo-Dur) and a newly designed sustained release tablet (E-0686) have been studied in fifteen healthy volunteers by measuring plasma and salivary concentrations. The theophylline level in saliva was 42.3 +/- 0.008 (s.e.m.) % of the plasma level and its correlation coefficient was 0.908. This observation suggests that salivary levels are considered to be a good indicator of the plasma concentration of theophylline. Interformulation variability in the saliva/plasma ratio was not significant in four occasions (p greater than 0.05). Thus, it was confirmed that the saliva/plasma ratio was nearly constant after administration of sustained release preparations of theophylline. Bioequivalency as to the extent of bioavailability of the two preparations was demonstrated by measurements of plasma and salivary levels. Compared to the theophylline levels in non-smokers, lower concentrations were observed in smokers at elimination phase by measurements of both the plasma and salivary levels, but shorter elimination half-life in smokers was indicated only in salivary data.