Improved long term stability of aqueous ethylcellulose film coatings: Importance of the type of drug and starter core

Instability during long term storage due to further gradual coalescence of the film remains one of the major challenges when using aqueous polymer dispersions for controlled release coatings. It has recently been shown that the addition of small amounts of poly(vinyl acetate)-poly(ethylene glycol)-graft-copolymer (PVA-PEC-graft-copolymer) to aqueous ethylcellulose dispersion provides long term stable drug release patterns even upon open storage under stress conditions in the case of theophylline matrix cores. However, the transferability of this approach to other types of drugs and starter cores exhibiting different osmotic activity is yet unknown. The aim of this study was to evaluate whether this novel approach is also applicable to freely water-soluble drugs and osmotically active sugar starter cores. Importantly, long term stable drug release profiles from coated diltiazem HCl-layered sugar cores could be achieved even upon open storage for 1 year under stress conditions (40 degrees C and 75% relative humidity). However, to provide desired drug release profiles the amount of added PVA-PEG-graft-copolymer must be adjusted. A minimal critical content of 10% (w/w) of this hydrophilic additive was identified, under which further polymer particle coalescence upon long term storage under stress conditions cannot be excluded. Potentially too rapid drug release can effectively be slowed down by increasing the coating level. Thus, adapting the polymer blend ratio and coating thickness desired and long term stable drug release profiles (even under stress conditions and open storage) can be provided for very different types of drugs and starter cores by the addition of small amounts of PVA-PEG-graft-copolymer to aqueous ethylcellulose dispersion. (C) 2008 Elsevier B.V. All rights reserved.