Characterization and solubility study of solid dispersions of flunarizine and polyvinylpyrrolidone

Flunarizine is a selective calcium entry blocker poorly water-soluble. In this report, the interactions of this drug with polyvinylpyrrolidone in solid dispersions, prepared according to the dissolution method using methanol as the solvent, have been investigated. For purposes of comparison physical mixtures were prepared by simple mixture and homogeneization of the two pulverized components. Combinations of flunarizine/polyvinylpyrrolidone of the following percentage proportions were prepared: 10/90, 20/80, 30/70, 40/60, 50/50, 60/40 and 80/20 (mean particle size of 0.175 mm). The physicochemical properties of solid dispersions were investigated with X-ray diffraction, infrared spectroscopy, differential scanning calorimetry and solubility in equilibrium. X-ray patterns and differential scanning calorimetry have shown that polyvinylpyrrolidone inhibits the crystallization of flunarizine when percentages drug/polymer are 10/90, 20/80 and 30/70. The infrared spectra suggest that there was no chemical interaction between flunarizine and polyvinylpyrrolidone. Equilibrium solubility studies showed that drug solubility was enhanced as the polymer content increased. In general, the solubility increase was greater in solid dispersions than in physical mixtures and the solubility in equilibrium for solid dispersions and physical mixtures at the same drug/polymer proportion showed significant differences (P < 0.05).