NIFEDIPINE LOADED-POLYMERIC MICROSPHERES - PREPARATION AND PHYSICAL CHARACTERISTICS

Nifedipine-loaded microspheres of cellulosic polymers were prepared by a solvent evaporation method. The goal of this work was to investigat e the influence of some process parameters on the physical characteris tics of microspheres (size, drug content, kinetics of release). It app eared from obtained results that mean diameter of microspheres increas ed with the viscosity of the dispersed organic phase. Drug incorporati on efficiency in ethylcellulose microspheres decreased when organic ph ase viscosity was increased. In the other hand, it was noted that drug loading efficiency could be enhanced by decreasing ethylcellulose/hyd roxypropylcellulose (EC/HPC) or ethylcellulose/hydroxypropylmethylcell ulose (EC/HPMC) ratios. Differential scanning calorimetry (DSC) thermo grams and RX diffraction spectres indicated that nifedipine was incorp orated in an amorphous state in the microspheres. All microspheres for mulations exhibited slow and S-shaped release profiles with poor disso lution efficiency. However, release from microspheres of EC/HPC and EC /HPMC was slower but more regular than that from microspheres of EC (N 10). It was also found that drug release was related to organic phase viscosity. Thus, in the case of EC, the higher was the viscosity of th e organic phase, the slower was the release kinetic. Whatever the micr ospheres formulation, release patterns didn't exhibit any burst effect indicating the absence of free nifedipine or crystals on the surface of the microspheres. Nifedipine release from microspheres was well des cribed by combined kinetics (zero- and first-order kinetics or zero-or der and Higuchi square-roots kinetics). (C) 1998 Elsevier Science B.V. All rights reserved.