Interaction of naproxen with noncrystalline acetyl beta- and acetyl gamma-cyclodextrins in the solid and liquid state.

Randomly acetylated, amorphous beta-cyclodextrin (AcbetaCd) and gamma-cyclodextrin (AcgammaCd), having an average substitution degree per anhydroglucose unit, respectively, of 1.1 and 0.95 (about 7.7 acetyl residues per macrocycle), were investigated for their interactions in the solid and liquid state with naproxen (NAP). Differential scanning calorimetry (DSC), supported by X-ray powder diffractometry (XRD), of NAP–AcbetaCd and NAP–AcgammaCd blends revealed an apparent decrease in drug crystallinity which was related to a heating-induced solid-state interaction between the drug and each carrier. A solubility of about 0.40 NAP mass fraction in amorphous AcbetaCd and amorphous AcgammaCd at room temperature was determined. Phase-solubility analysis at 25, 37, and 45°C accounted for AL-type inclusion complexation of NAP with AcbetaCd and AcgammaCd and revealed a solubilizing efficiency of AcbetaCd toward NAP about 4 times that of AcgammaCd. Equimolar drug–carrier combinations prepared from the respective blends by grinding, kneading, coevaporation and freeze-drying were characterized by DSC and XRD and tested for dissolution rate of NAP using the
dispersed amount and continuous flow through methods. The best performance in terms of dissolution rate enhancement (about 23 times and about 10 times the dissolution efficiency of pure drug in the dispersed amount and continuous flow through tests, respectively) was displayed by the NAP–AcbetaCd colyophilized product.