Water–Tween 40®/Imwitor 308®–isopropyl myristate microemulsions as delivery systems for ketoprofen: Small-angle X-ray scattering study

Small-angle X-ray scattering technique has been used to study the structural properties of the quaternary microemulsion Tween 40®/Imwitor 308®/isopropyl myristate/water and of five-component system obtained by the addition of the drug ketoprofen to the original quaternary system. The results enlighten the structuration of the studied systems and represent new complementary findings to the previous study [Podlogar, F., Bešter-Rogač, M., Gašperlin, M., 2005. The effect of internal structure of selected water–Tween 40 (R)–Imwitor 308 (R)–IPM microemulsions on ketoprofene release. Int. J. Pharm. 302, 68–77] on the correlation between the structuration of these systems and the release rates of the ketoprofen. The present results indicate that in the samples with the moderate to high concentration of water where the latter is a continuous phase the addition of smaller amounts of the ketoprofen does not change their inner structuration significantly. The quaternary sample containing 46.2 wt.% of water seems to be very near the composition where the transition from the bicontinuous to the lamellar structure of the microemulsion occurs. In the samples containing from 46.2 to 62.7 wt.% of water the swelling of lamellar phases with constant thickness of double-layer can be characterized. At approximately the latter composition another noticeable transition in the inner structuration of the microemulsion has been observed. Interestingly, all these changes in the inner structuration of the studied systems did not affect the trend of the drug release rates in this regime of water concentrations.