Dissolution of theophylline from sustained-release dosage forms and correlation with saliva bioavailability parameters.

Correlation between in vitro dissolution characteristics and in vivo salivary bioavailability parameters of four commercial sustained-release and one immediate-release theophylline (TP) or aminophylline dosage forms were examined. Area under the saliva concentration-time curve up to 6 h (AUC0----6), peak saliva concentration (Cmax), and fraction absorbed in 1 h (F1), based on saliva concentration following oral administration of TP or aminophylline dosage forms to five volunteers, were closely correlated with percents dissolved in pH 6.8 buffer in 30 min, D30 (6.8), or 60 min, D60 (6.8). Dissolution study in pH 6.8 buffer seemed to be a useful tool for development, evaluation, and quality control of sustained-release dosage forms of TP, since the saliva concentration was reported to represent the blood concentration of TP indirectly.