Effect of hydroxypropyl-beta-cyclodextrin and pH on the solubility of levemopamil HCl.

Levemopamil was solubilized by varying the concentration of hydroxypropyl-beta-cyclodextrin (HPbetaCD) and by the alteration of pH. The drug molecule has two sites for possible complexation with HPbetaCD, creating the possibility of either 1:1 or 1:2 complexation. The solubility as a function of HPbetaCD concentration of the charged and uncharged forms of the drug follows the A(L) and Ap complexation models, respectively. This suggests that the charged drug forms a 1:1 complex, whereas the neutral drug forms both 1:1 and 1:2 complexes.