In this work, the potential of waxes for preparing with the ultrasonic spray congealing technique microparticles for
controlling the in vitro release of verapamil HCl was investigated. The first part of the study encompassed the optimisation
of the formulation to achieve an efficient drug incorporation together with a satisfactory in vitro drug release rate. In
particular, microcrystalline wax, stearyl alcohol and mixtures of the two were used. Also a surfactant (soya lecithin) was
added to the formulations. After the particle size analysis, the characterisation of the microparticles involved the study of the
solid state of drug and carriers in the systems (DSC, HSM and XRD) and the morphological and chemical analyses of the
microparticle surface (SEM and XPS). Finally, the drug release mechanism from these devices was evaluated using the
statistical moment analysis. The results of this study show that by selecting the type and the amount of the carriers,
microparticles with a spherical shape and a good encapsulation efficiency were observed. These particles showed a
zero-order release for 8 h, without modifying the solid state properties of the drug. Therefore, waxy microparticles prepared
by the ultrasonic spray congealing technique are promising solvent-free devices for controlling the release of verapamil HCl.
2003 Elsevier Science B.V. All rights reserved.
