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 (approximately 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 approximately 0.40 NAP mass fraction in amorphous AcbetaCd and amorphous AcgammaCd at room temperature was determined. Phase-solubility analysis at 25, 37, and 45 degrees C accounted for A(L)-type inclusion complexation of NAP with AcbetaCd (K(1:1,25 degrees C)=4.5(4) x 10(3) l mol(-1)) and AcgammaCd (K(1:1,25 degrees C)=0.80(7) x 10(3) l mol(-1)) and revealed a solubilizing efficiency of AcbetaCd toward NAP approximately 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 (approximately 23 times and approximately 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.