Characterization of a pseudo ternary phase diagram of poloxamer 407 systems for potential application of 5-aminolevulinic acid in photodynamic therapy.

A poloxamer 407 (POX) gel containing dimethyl isosorbide (DMIS), isopropyl alcohol (IPA), propylene glycol dicaprylocaprate (MIG) and water has been suggested in a previous study for permeation enhancement of 5-aminolevulinic acid (ALA) across isolated human stratum corneum. The purpose of this study was to characterize other formulations coming from the same pseudo ternary phase diagram as the "Thermogel" in order to find out which of them show appropriate characteristics to be used as a vehicle for ALA since it could be shown that variation of the ingredients' content had an influence on the permeation rate. A pseudo ternary phase diagram was developed with water, a fixed combination of 1:1 of IPA and DMIS and a fixed ratio of 4:1 POX to MIG. The systems were categorized according to their consistencies and ringing gel characteristics with special emphasis on appropriate formulations for dermal application. Polarizing microscopy enabled a clear differentiation between isotropic and anisotropic systems. Wide angle X-ray diffraction analyzes confirmed that anisotropy was due to crystalline POX. Furthermore both methods showed that IPA/DMIS was an inferior solvent mixture for POX related to water.