Influence of Physicochemical Interactions on the Properties of Suppositories. III. Reeological Behaviour of Fatty Supfository Bases and its Effect on Spreading in Rats

Abstract

The viscosity and other rheological properties of the molten base at rectal temperature can markedly affect the rate of release and absorption of drugs' from fatty suppositories. The rheograms of pure mono-acid triglycerides, their mixtures and triglyceride suppository bases were determined at various temperatures using a rotational rheometer. Completely molten systems gave Newtonian behaviour, while incompletely molten mixtures, containing a suspension of higher melting triglyceride, exhibited plastic behaviour with thixotropy which reverted to Newtonian behaviour on removal, dissolution or melting of the higher melting component, The plastic yield values (67 Nm⁻²) were less tnan the reported rectal pressure (300 Nm⁻²), suggesting that they exert little effect on spreading in the rectum.