Studies on Pharmaceutical Drug Design for Suppositories. II. Rheological Properties of Emulsion-Type Suppository Bases

The rheological characteristics of emulsion bases must be chosen so as to produce a suppository having optimum physical, chemical and pharmacological properties. In this study, we measured some rheological characteristics of the emulsion in order to find favorable physicochemical conditions for the preparation of emulsion-type bases. The suppository consisted of Witepsol S-55, aqueous polymer, Amisoft surfactant and water. The preparation procedure was that described in our previous paper. The vicosity and visco-elasticity of suppository bases were measured with a Vismetron and an RM-1 or RV-12 type rheometer. Amisofts had excellent rheological properties as surfactants for emulsion-type suppository bases, as compared with sodium dodecyl sulfate or Tween 80. The activation energy of viscosity increased gradually at first and then sharply with increasing volume concentration of the dispersed phase after passing through the 50% point. The change in the activation energy was substantial when the volume concentration rose over 60%.