H. Tomida et al., PREPARATION OF THEOPHYLLINE-LOADED CALCIUM ALGINATE GEL CAPSULES AND EVALUATION OF THEIR DRUG-RELEASE CHARACTERISTICS, Chemical and Pharmaceutical Bulletin, 41(12), 1993, pp. 2161-2165
A method for the preparation of theophylline-loaded alginate gel capsu
les was developed, and their drug release characteristics were investi
gated. A dispersion containing theophylline and wheat starch suspended
in a calcium chloride solution was dropped into a sodium alginate sol
ution. The calcium ions then diffused out of the droplets and reacted
with the alginate, resulting in the formation of a water-insoluble cal
cium alginate gel membrane around each droplet. In subsequent drying,
spherical, glossy capsules with a smooth surface were obtained (an ave
rage diameter of 3.1 mm). The coat thickness increased with coating ti
me, and the CaCl2, concentration in the core dispersion increased. The
efficiency of drug encapsulation (EE) decreased with an increase of t
he coating time, and increased with an increase of the CaCl2, concentr
ation and the theophylline loading dose in the core dispersion. The co
at thickness and EE were almost independent of the sodium alginate con
centration in coating fluids (1% and 2%). The theophylline release fro
m the gel capsules followed zero-order kinetics, and the release rates
were significantly reduced as the coat thickness increased. Furthermo
re, the release rates were greatly reduced compared with those of the
matrix-type alginate gel beads.