Properties of theophylline tablets dry powder coated with Eudragit E PO and Eudragit L 100-55.

The aim of the present study was to investigate the influence of Eudragit E PO on the drug release mechanism of Eudragit L 100-55 film coatings applied to theophylline tablets by a dry powder coating technique. The process was entirely liquid-free. Calculation of the Flory-Huggins interaction parameter based on solubility parameters suggested immiscibility of the two copolymers. MDSC thermograms were characterized by two glass transitions for the investigated Eudragit E PO/Eudragit L 100-55 ratios and confirmed incomplete miscibility of the copolymers at processing conditions. FT-IR analysis was employed to study binding interactions of the polymers. Due to the higher affinity of the plasticizer, triethyl citrate, for Eudragit E PO compared to Eudragit L 100-55, redistribution of the plasticizer was observed during the curing phase of the process. Plasticizer migration also affected the initial phase of drug release from powder-coated theophylline tablets that were stored for four weeks. Drug release from powder-coated tablets was dependent on the polymer blend ratio, coating thickness, and the pH of the dissolution medium. A broad range of pH dependent theophylline release profiles were obtained as a function of the polymer blend ratio. The particle size of the coating powder influenced the microstructure of the film coating.