title: Preliminary evaluation of an aqueous wax emulsion for controlled-release coating.
abstract: The purpose of this work was to evaluate the use of an aqueous carnauba wax emulsion (Primafresh HS, Johnson Wax) in a spray-coating process. This involved assessing the effectiveness of the wax in sustaining the release of the drug, theophylline. Second, the process by which the drug was released from the wax-coated pellets was modeled. Finally, a method to determine the optimum blend of pellets with different wax thicknesses, in order to yield a zero-order release profile of the drug, was addressed. Nonpareil pellets were loaded with theophylline using a novel powder coating technique. These drug-loaded pellets were then coated with different levels of carnauba wax in a 6-in. diameter Plexiglas fluid bed with a 3.5-in. diameter Wurster partition. Drug release was measured using a spin-filter dissolution device. The study resulted in continuous carnauba wax coatings which showed sustained drug release profile characteristics typical of a barrier-type, diffusion-controlled system. The effect of varying wax thickness on the release profiles was investigated. It was observed that very high wax loadings would be required to achieve long sustained-release times. The diffusion model, developed to predict the release of the drug, showed good agreement with the experimental data. However, the data exhibited an initial lag-time for drug release which could not be predicted a priori based on the wax coating thickness. A method of mixing pellets with different wax thicknesses was proposed as a way to approximate zero-order release.
authors.affiliation: Department of Chemical Engineering, College of Engineering and Mineral Resources, West Virginia University, Morgantown 26506-6102, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Walia
authors.forename: P J
authors.initials: PJ
authors.lastname: Stout
authors.forename: R
authors.initials: R
authors.lastname: Turton
mesh_terms: D004655:Emulsions; D005069:Evaluation Studies as Topic; D008956:Models, Chemical; D013806:Theophylline / Q000008:administration & dosage*; D014885:Waxes
chemical_list: D004655:Emulsions; D014885:Waxes; D013806:Theophylline