Preparation of Theophylline-Loaded Calcium Alginate Gel Capsules and Evaluation of Their Drug Release Characteristics

Abstract

A method for the preparation of theophylline-loaded alginate gel capsules was developed, and their drug release characteristics were investigated. A dispersion containing theophylline and wheat starch suspended in a calcium chloride solution was dropped into a sodium alginate solution. The calcium ions then diffused out of the droplets and reacted with the alginate, resulting in the formation of a water-insoluble calcium alginate gel membrane around each droplet. In subsequent drying, spherical, glossy capsules with a smooth surface were obtained (an average diameter of 3.1 mm). The coat thickness increased with coating time, and the CaCl2 concentration in the core dispersion increased. The efficiency of drug encapsulation (EE) decreased with an increase of the coating time, and increased with an increase of the CaCl2 concentration and the theophylline loading dose in the core dispersion. The coat thickness and EE were almost independent of the sodium alginate concentration in coating fluids (1% and 2%). The theophylline release from the gel capsules followed zero-order kinetics, and the release rates were significantly reduced as the coat thickness increased. Furthermore, the release rates were greatly reduced compared with those of the matrix-type alginate gel beads. © 1993, The Pharmaceutical Society of Japan. All rights reserved.