Design and in vitro evaluation of a film-controlled dosage form self-converted from monolithic tablet in gastrointestinal environment.

The purpose of this study is to design an easily manufactured sustained drug delivery system, which can be converted to a film coated system during the dissolution process and then control the drug release according to near zero-order kinetics. Two kinds of pH-sensitive and oppositely charged hydrophilic polymers, chitosan and alginate, were physically mixed as the matrix. Slightly water-soluble drugs such as theophylline, aspirin, and acetaminophen were utilized as model drugs. In vitro drug release and swelling tests were undertaken in simulated gastrointestinal environments. The formation and properties of the film formed during the dissolution process were identified using different techniques. It was demonstrated that formation of the film was based on the interaction of the polymers on tablet surface with the change of system pH. In 0-4 h drug release depended on the intrinsic properties of the polymers, however, characteristics of the film played a leading role in controlling drug release after 4 h. By studying the ratio of relaxation over Fickian diffusion and relationship between tablets swelling and drug release, it was revealed that the film probably modified drug release behavior by limiting polymer erosion. The in vivo behavior of this hydrophilic matrix system will be investigated.