Propranolol forms affect properties of Carbopol-containing extruded-spheronized beads

Drug release rates from extruded-spheronized beads containing Carbopol have been shown to be dependent on the chemical nature of different types of drugs. To further clarify solubility, salt counterion, pH, and ionic strength effects on Carbopol bead characteristics, including but not limited to the drug release profile, the present study utilizes propranolol in its free base, hydrochloride, and maleate forms. Different forms of propranolol resulted in different bead average diameter, roundness, and smoothness, but the ruggedness was not affected. Release profiles for the two salt forms were nearly superimposable, but the free base form was released more slowly. Mathematical analysis of the release data revealed that Fickian diffusion and polymer relaxation were contributing factors to the release mechanism in each case, although polymer relaxation was more influential with the free base form. In light of these results, the choice of the form of a drug should be considered carefully when preparing Carbopol-containing beads produced by extrusion-spheronization.