Release rates of ketoprofen from poloxamer gels in a membraneless diffusion cell.

Release rates of ketoprofen from topical gels consisting of poloxamer 407 were evaluated using a membraneless diffusion cell with isopropyl myristate as the receptor medium. The effects of formulation variables such as polymer content (20-30%), drug (0.2-3.0%) and ethanol (0-20%) concentrations, pH (3.0-6.0), and temperature of the gels (25-45 degrees C) on drug release were studied. Release of ketoprofen from the gel decreased exponentially as the polymer concentration increased. Over the temperature range studied, the drug release rate appeared to correlate with the Arrhenius function. The change of the gel pH from 3 to 6 substantially increased the release rate of ketoprofen. The enhanced drug release in the presence of ethanol is attributed to the decrease in viscosity of the gel. With higher drug loading in the gel, an increase in the release rate, but a reduction of diffusion coefficient of the drug, was observed.