Studies on the In Vitro Release of Theophylline from Polyethylene Glycol-Polyvinyl Acetate Mixtures Liquid Filled into Hard Gelatin Capsules

The release of theophylline from mixtures of polythylene glycol (PEG) with polyvinyl acetate (PVAc) liquid filled into hard gelatin capsules has been studied in vitro. Results indicate that theophylline release can be controlled over a relative wide range by varying the concentration of PVAc, and that the reproducibility of the release profile is improved considerably if the PVAc concentration exceeds 2% w/w. Other results show that drug load, molecular weight of PEG, and pH of the dissolution medium also affect release profiles. In general, the experimental data are well described by a simple equation derived from Fickian diffusion kinetics, thus supporting the suggestion that drug release from this type of formulation is controlled by diffusion in solution through water-filled pores in a network of precipitated PVAc.