A Study on the Manufacture and in Vitro Dissolution of Terbutaline Sulfate Microcapsules and their Tablets

Abstract

Microcapsules of terbutaline sulfate with cellulose acetate butyrate and ethylcellulose were prepared using an emulsion-solvent evaporation technique. The in vitro dissolution of terbutaline sulfate was studied using the USP rotating basket method. As the polymer to drug ratio increased, the microcapsule size distribution shifted to the smaller size and the release of terbutaline sulfate decreased. The release of terbutaline sulfate was independent of the dissolution medium pH for both polymers. The release kinetics from the microcapsules was dependent on the polymer type and polymer to drug ratio. The release of terbutaline sulfate from cellulose acetate butyrate and ethylcellulose microcapsules formulated with a 1:1 polymer to drug ratio was complex and could not be differentiated between the square-root of time and first-order release models. However, the square-root of time model was followed by microcapsules formulated with a 2:1 or a 3:1 cellulose acetate butyrate to drug ratio. When the ethylcellulose to drug ratio was increased to 2:1 the square-root of time model was followed. At an ethylcellulose to drug ratio of 3:1 the release kinetics could not be differentiated between the Hixon-Crowell and first-order release models. The T50% from ethylcellulose microcapsules was decreased when the microcapsules were compressed into tablets with the addition of Avicel^R/Emcompress^R (2:1) or Avicel^R.