Investigation and physicochemical characterization of vinpocetine-sulfobutyl ether beta-cyclodextrin binary and ternary complexes

The purpose of this study was to investigate the interactions between vinpocetine (VP), sulfobutyl ether beta-cyclodextrin (SBEbetaCD) and the water-soluble polymers polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC). The water-soluble polymers were shown to improve the complexation efficiency of SBEbetaCD, and thus less SBEbetaCD was needed to prepare solid VP-SBEbetaCD complexes in the presence of the polymers. The interactions between VP and SBEbetaCD, with or without PVP or HPMC, were thoroughly investigated in aqueous solutions using the phase-solubility method as well as in the solid state. The amount of VP solubilized in water or aqueous polymer solution increased linearly with increasing SBEbetaCD concentration, demonstrating A(L)-type plots. We estimated the apparent stability constant (K(c)) at room temperature of VP-SBEbetaCD binary complex to be 340 M(-1) and this value increased to 490 M(-1) or 390 M(-1), respectively, with the addition of PVP and HPMC, assuming a 1 : 1 VP-SBEbetaCD molar ratio. Improvement in the K(c) values for ternary complexes clearly confirmed the benefit of the addition of water-soluble polymers to promote higher complexation efficiency. Solid VP-SBEbetaCD binary and ternary systems were prepared by physical mixing, kneading, coevaporation, and lyophilization methods and fully characterized by scanning electron microscopy, differential scanning calorimetry, and X-ray diffractometry. The results obtained suggest that coevaporation and lyophilization methods yield a higher degree of amorphous entities and indicated formation of VP-SBEbetaCD binary and ternary complexes.