Hydroxypropyl-β-cyclodextrin: preparation and characterization; effects on solubility of drugs

Conditions for condensation of β-cyclodextrin with propylene oxide were found which give preparations of hydroxypropyl-β-cyclodextrin with a narrow and symmetrical distribution of the degree of substitution. Furthermore, methods for purification of hydroxypropyl-β-cyclodextrins from the contaminating oligopropylene glycols were developed. Preparations of hydroxypropyl-β-cyclodextrin with low degrees of substitution ( < 8) were found to have optimal solubilization properties for drugs and also these preparations could be transformed into non-hygroscopic powders; the preparations with higher degrees of substitution (12–14) were semi-solids of lower solubilization power. The solubilities of 32 drugs in concentrated aqueous solutions of hydroxypropyl-β-cyclo-dextrins (40–50%) were measured; some of these were improved by three orders of magnitude over the corresponding solubilities in water.