Diclofenac-beta-cyclodextrin binary systems: physicochemical characterization and in vitro dissolution and diffusion studies

The aim of this work was to study the influence of β-cyclodextrin (β-CD) on the biopharmaceutic properties of diclofenac (DCF). To this purpose the physicochemical characterization of diclofenac-β-cyclodextrin binary systems was performed both in solution and solid state. Solid phase characterization was performed using differential scanning calorimetry (DSC), powder x-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). Phase solubility analyses, and in vitro permeation experiments through a synthetic membrane were performed in solution. Moreover, DCF/β-CD interactions were studied in DMSO by 1H nuclear magnetic resonance (NMR) spectroscopy. The effects of different preparation methods and drug-to-β-CD molar ratios were also evaluated. Phase solubility studies revealed 1: 1 M complexation of DCF when the freeze-drying method was used for the preparation of the binary system. The true inclusion for the freeze-dried binary system was confirmed by 1H NMR spectroscopy, DSC, powder XRD, and IR studies. The dissolution study re-yealed that the drug dissolution rate was improved by the presence of CDs and the highest and promptest release was obtained with the freeze-dried binary system. Diffusion experiments through a silicone membrane showed that DCF diffusion was higher from the saturated drug solution (control) than the freeze-dried inclusion complexes, prepared using different DCF-β-CD molar ratios. However, the presence of the inclusion complex was able to stabilize the system giving rise to a more regular diffusion profile.