Dissolution and diffuse reflectance characteristics of coated theophylline particles

The aim of the present study was to investigate how the dissolution and diffuse reflectance characteristics of theophylline microcapsules were influenced by the changes in the thickness and by the plasticizer content of coating. Microencapsulation was carried out in laboratory fluidized-bed system using water dispersable Eudragit-type film coating polymer. United States Pharmacopeia rotating paddle method was applied for the in vitro dissolution study. The dissolution profile of the produced microcapsules was evaluated by Weibull distribution. The effect of the thickness of coating and that of the plasticizer content on the dissolution kinetics was modelled by a second-order polynomial equation fitted to the data gathered by a face-centered central composite statistical design. It was found that both of the examined coating parameters influenced the drug release kinetics. The diffuse reflectance spectra of the coated particles indicated the changes in coating parameters without destructive analysis of samples. (C) 1997 Elsevier Science B.V.