Complexation of nevirapine with β-cyclodextrins in the presence and absence of Tween 80: characterization, thermodynamic parameters, and permeability flux

The work is undertaken to evaluate the effect of Tween 80 on the complexing ability of beta-cyclodextrins to encapsulate the poorly soluble antiretroviral agent, nevirapine. The phase solubility diagram indicates 1:1 stoichiometry and is supported by electronspray ionization mass spectrometry. The complexes were characterized by DSC, FT-IR, and XRD in the solid state. The ternary systems were autoclaved before being lyophilized for the best results. Proton NMR suggests that the methyl pyridine ring of the drug is involved in inclusion and enters from the wider side of the cavity which was confirmed by COESY NMR. Solution calorimetry, a direct method to determine the thermodynamic parameters, was used to determine the complexation constant (K) and other thermodynamic properties. The process is associated with negative a dagger H and positive a dagger S indicating a stable inclusion complex. The value of K follows the order beta-CD < HP-beta-CD < M-beta-CD. The molar enthalpy of solution in autoclaved solid formulation is less endothermic as compared to additive molar enthalpy of solution obtained by summation of enthalpy of solution of individual components suggesting synergistic interaction between the drug and its constituents. A threefold increase of the in vitro permeability flux was observed for binary systems which was elevated to fourfold for autoclaved ternary complexes.