GELATIN GELS AND POLYOXYETHYLENE-POLYOXYPROPYLENE GELS - COMPARATIVE-STUDY OF THEIR PROPERTIES

Gelatine gels and polyoxyethylene-polyoxypropylene (Pluronic(R)) F-108 and F-127 gels were prepared at concentrations ranging between 5 and 25 % (W/V), the former by dispersion at 37 degrees C, the later by dis persion at 4 degrees C. The viscosity, the gel-sol transition temperat ure and the ''in vitro'' release kinetics of these gels were compared as a first step for the elaboration of parenteral controlled release f ormulations. Phenolsulphonftaleine (PR) was used as a tracer. In all c ases the viscosity increased with the rise in the concentration of gel atin (20 to 264 cps for 5 to 20 %) or pluronic (260 and 1,520 cps for 20 and 25 % F-108). The gel-sol transition temperature for gelatine ge ls was directly related to the concentration. On the contrary, for plu ronic gels an inverse relation was observed, being the gel-sol transit ion temperature higher in copolymers with a large percentage of polyox yethylene groups (30+/-0.2 degrees C for 25 % F-108). In both types of gels, a rise in pH and ionic strength decreased the gel-sol transitio n temperature, whereas PR increase this temperature. The release of th e tracer, from the gels to the aqueous medium, showed a zero-order kin etics and the release rates were inversely proportional to the concent ration of gelling agent.