Formulation, preparation and dissolution characteristics of propranolol hydrochloride microspheres

Propranolol HCl was encapsulated with cellulose acetate butyrate (CAB) by an emulsion-solvent evaporation method to obtain discrete, spherical microspheres. The effects of drug to polymer ratio and microsphere size on dissolution characteristics were studied. Drug release was faster in simulated intestinal fluid than in simulated gastric fluid. Unencapsulated propranolol HCl powder had very rapid dissolution, as expected. Release rate from CAB microspheres increased with higher drug to polymer ratios and decreased with increasing diameter. Drug release from microspheres sizes larger than 180 microns was reasonably well described by the spherical matrix model. For microsphere size fractions between 127 and 359 microns the relationship between the 50 per cent release time and the square of the microsphere diameter was linear (r = 0.9999).