Physicochemical and release studies of naproxen in poloxamer gels

The solubility of naproxen at pH 2 was significantly increased as a linear function of PF-127 concentration at three temperatures. Naproxen was highly entrapped by the micelles as indicated by large partition coefficients. The micellar solubilization was a spontaneous (Delta G < 0) and exothermic (Delta H < 0) process which resulted in a less orderly state (Delta S > 0). In the presence of PF-127, the release of naproxen across the membrane was significantly sustained at pH 2 and inversely proportional to the surfactant concentration. At pH 7, PF-127 had little effect on the membrane transport of naproxen. The release of naproxen from the PF-127 gel into isopropyl myristate was dependent on the medium pH. The highest release was observed at pH 6.3. The diffusion coefficients of naproxen were inversely proportional to drug loading and PF-127 concentration. The activation energy of 7.45 kcal/mol for the diffusion of naproxen in the gel was calculated using the Arrhenius equation.