Microencapsulation of lipophilic drugs in chitosan-coated alginate microspheres

Chitosan-coated alginate microspheres containing a lipophilic marker dissol ved in an edible oil, were prepared by emulsification/internal gelation and the potential use as an oral controlled release system investigated. Micro sphere formation involved dispersing a lipophilic marker dissolved in soybe an oil into an alginate solution containing insoluble calcium carbonate mic rocrystals. The dispersion was then emulsified in silicone oil to form an O /W/O multiple phase emulsion. Addition of an oil soluble acid released calc ium from carbonate complex for gelation of the alginate. Chitosan was then applied as a membrane coat to increase the mechanical strength and stabiliz e the microspheres in simulated intestinal media. Parameters studied includ ed encapsulation yield, alginate concentration, chitosan molecular weight a nd membrane formation time. Mean diameters ranging from 500 to 800 mu m and encapsulation yields ranging from 60 to 80% were obtained. Minimal marker release was observed under simulated gastric conditions, and rapid release was triggered by transfer into simulated intestinal fluid. Higher overall l evels of release were obtained with uncoated microspheres, possibly due to binding of marker to the chitosan membrane coat. However the slower rate of release from coated microspheres was felt better suited as a delivery vehi cle for oil soluble drugs. (C) 1999 Elsevier Science B.V. All rights reserv ed.