Effect of PVP K-25 on the formation of the naproxen:β-ciclodextrin complex

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The aim of this study was to investigate the effects of the presence of the water-soluble polymer polyvinylpyrrolidone K-25 (MW=24,000 g/mol) on the complexation of the AINE naproxen, in its sodium salt form, with the β-cyclodextrin.The data revealed that the polyvinylpyrrolidone K-25 interacts with the drug as well as with the drug:β-cyclodextrin inclusion complex. The polymer shows more affinity for the inclusion complex, K=(6.67±0.292)×10−5 M−1 than for the free drug, (2.08±0.208)×10−5 M−1.The presence of different proportions of polymer, in a range 0–1% (w/w) of polyvinylpyrrolidone, does not increase the ability of drug–cyclodextrin complexation but important changes in the driving force of complex formation were detected, depending on the percentage of polyvinylpyrrolidone K-25 present. At low polymer concentrations, the complexation process is driven entropically, while at higher PVP proportions it is enthalpically favored.In the ternary system, polyvinylpyrrolidone K-25 partially or totally coats the drug:β-cyclodextrin inclusion complex interacting with the β-cyclodextrin (through hydrogen bonds), and with the naproxen.

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