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 degrees 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 degrees 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.