Comparison of gastroretentive microspheres and sustained-release preparations using theophylline pharmacokinetics

The objective of this study was to use the pharmacokinetics of theophylline to compare various gastroretentive microspheres. Three types of theophylline microspheres prepared from a hydrophobic dextran derivative were characterized in terms of drug release in-vitro and floating and mucoadhesive properties. Theophylline pharmacokinetic studies were conducted in Beagle dogs, comparing bulk powder, commercial sustained-release granules (Theodur), sustained-release microspheres, floatable microspheres and mucoadhesive microspheres. Theodur and sustained-release microspheres resulted in a lower maximum concentration (Cmax) (P < 0.01) and larger values for mean residence time (MRT) (P < 0.05) than bulk powder, whereas area under the concentraion-time curve (AUC) were lower. The floatable microspheres showed a larger value for MRT than bulk powder (P < 0.01), and a larger AUC than Theodur (P < 0.05). The pharmacokinetic parameters of the mucoadhesive microspheres indicated an increase in AUC without decreasing the rate of bioavailability. Overall, the gastroretentive microspheres improved the extent of bioavailability of theophylline, which is absorbable from the entire gastrointestinal tract. The mucoadhesive microsphere showed a prolonged serum drug level, indicating a superior sustained-release delivery system for theophylline.