Influence of hydroxyethylcellulose on the drug release properties of theophylline pellets coated with Eudragit® RS 30 D

The objective of this study was to investigate the influence of a hydrophilic polymer, hydroxyethylcellulose (HEC), on the release properties of theophylline from pellets coated with Eudragit® RS 30 D, and the physicochemical properties of Eudragit® RS 30 D cast films. The release rate of theophylline from Eudragit® RS 30 D coated pellets decreased during storage at 25 °C/60% RH due to the further coalescence of colloidal acrylic particles. In addition, water-vapor permeability and tensile strength of Eudragit® RS 30 D cast film decreased after 1-month storage at 25 °C/60% RH. The presence of 10% hydroxyethylcellulose in the coating formulation was shown to stabilize the drug release rate from coated pellets, the water-vapor permeability and the tensile strength of free films. Atomic force microscopy and scanning electronic microscopy were used to demonstrate that the HEC was immiscible with Eudragit® RS 30 D in the cast films. The stabilization effect of HEC was investigated and determined to be due to the formation of an incompatible phase between the latex particles which impaired further coalescence of the colloidal acrylic particles.