Rheological study of rectal formulations of sodium valproate

Abstract

The importance of the spreading capacity of the suppository base in the rectal ampulla makes it important to determine dynamic viscosity of lipophilic excipients and to characterize the changes in their rheological properties caused by the addition of other components. We evaluated the influence of colloidal silica (Aerosil R 972), Span 80 and sodium valproate on the excipients Witepsol H-15 and Suppocire AS₂. Subsequent analyses in rabbits established the correlation between viscosity of the suppository mass after melting and the release and absorption of drugs administered rectally. The results show that excipients with initially dilating flow subsequently showed plastic flow characteristics, with marked thixotropy and increased viscosity which delayed release and absorption.