Solubilization of flavopiridol by pH control combined with cosolvents, surfactants, or complexants

This study investigates the roles of both ionized and unionized species of flavopiridol in solubilization by complexation, micellization, and cosolvency. Control of pH was used in combination with surfactants (polysorbate 20 and polysorbate 80), cosolvents (ethanol and propylene glycol), as well as uncharged and anionic complexing agents [hydroxypropyl β-cyclodextrin (HPβCD) and sulfobutyl ether β-cyclodextrin (SBEβCD)] to solubilize flavopiridol. These combined techniques increase not only the solubility of the un-ionized flavopiridol but also the solubility of the ionized drug. This study confirms that previously developed equations effectively characterize the roles of pH, pk(a), and either complexation constant, micelle partition coefficient, or cosolvent solubilizing power in determining drug total aqueous solubility.