VEHICLE INFLUENCE ON IN-VITRO RELEASE OF METRONIDAZOLE - ROLE OF W/O/W MULTIPLE EMULSION

Few studies have been made on the topical administration of w/o/w multiple emulsions, although their advantages in the controlled release by oral and parenteral administration have already been shown. The objective of this study was to compare the in vitro release of a hydrosoluble molecule (metronidazole) from w/o/w multiple, w/o and o/w emulsions. In order to avoid any influence of the formulation, all emulsions were prepared according to the same formula. The microscopic aspect, conductivity values and theological parameters confirmed that three emulsion types were obtained. Metronidazole release was studied on synthetic membranes and on rat skin biopsies. When the synthetic membrane offered negligible resistance to passage of the drug (cellulose membrane), metronidazole release from the w/o/w emulsion was slightly slower compared with the o/w emulsion, while much slower release was observed with the w/o emulsion. When the synthetic membrane was rate-controlling diffusion (silicone), the difference between the emulsions was decreased, although the rank order remained the same. In the case of skin, the absorption of metronidazole is similar from w/o/w and o/w emulsions, however, it is faster from these two emulsions than from the w/o emulsion.