Influence of surfactants, polymers, and concentration of the water phase on in vitro drug release from emulsion-type suppositories.

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Abstract
Generally, drug release from the base is considered to be one of the most important parameters in evaluating the pharmaceutical usefulness of suppositories in vivo and in vitro. In spite of the therapeutic importance and wide applications of suppositories, the absorption mechanisms and the factors determining their absorption characteristics have not been established. The present study was undertaken to investigate the effects of surfactants, polymers and concentration of the water phase on in vitro drug release emulsion-type suppositories. N1-(2''-furanidyl)-5-fluorouracil (FT-207), theophylline and indomethacin were chosen as model compounds. In order to clarify the behavior of the rat rectal membrane, the following 3 different methods for studying drug release (in vitro) were selected: the filter membrane technique; the use of membranes of animal origin; and in situ rectal recirculation technique. In the case of readily water-soluble compounds such as FT-207, the amount of drug released increased with increase of the water content in the suppository base. No significant effect of concentration of the water phase in the suppository base was found for fatty drugs such as indomethacin. By the addition of aqueous polymer, the amount of drug released could be controlled and the release prolonged in the emulsion-type suppository base.