An inclusion complex of fluticasone propionate with γ-cyclodextrin in aqueous solution and in a solid state

Inclusion complex formation of fluticasone propionate (FLT) with γ-cyclodextrin (γ-CD) in aqueous solution and in a solid state was confirmed by the solubility method and powder X-ray diffractometry. A solid complex of FLT with γ-CD (FLT/γ-CD) was prepared by a coprecipitation method, and its dissolution behavior in water was examined in comparison with FLT. Phase solubility diagrams obtained for FLT/α-CD, FLT/β-CD, and FLT/γ-CD systems in water at 26 °C were Ap-, AL-, and Bs-type phase diagrams, respectively. The apparent stability constants, K′, of FLT/β-CD and FLT/γ-CD from the initial straight line portion of the solubility diagram were 10,003 M−1 and 1257 M−1, respectively. The FLT content of the solid complex of FLT/γ-CD was 16.18%. The stoichiometry of the complex was found to be 1:2 (molar ratio, FLT:γ-CD), which is in good accordance with that based on the data in the plateau region of the solubility diagram. The solubility values for FLT in the solutions at 10 mM of α-, β-, and γ-CD at 26 °C were 0.3, 1.4, and 78.3 μg/mL, respectively. Those values were higher than that of FLT, 0.1 μg/mL, in water at 37 °C. The dissolution rate of FLT was remarkably improved by FLT/γ-CD.