- 17 Downloads
Physicochemical theories on the stability of particles against agglomeration, the behaviour of particles at the interface and dissolution appeared to act as powerful tools in predicting the rate controlling steps in the model system used. For such a prediction only basic physicochemical properties of the system involved, which are available in the literature or can easily be measured, have to be known. In the present study not only the primary particle size, but also the agglomeration behaviour and therefore the concentration were important factors, particularly when transport to the interface was the rate-limiting step. But, the initial release rate became independent of particle size and concentration when dissolution at the interface limited the rate. Additives present in low concentrations had a decisive influence on the behaviour of the particles in the suspension and at the interface, and thus on the dissolution rate. The relevance of this model study for the design and development of rectal dosage forms is that an insight has been gained into the basic mechanisms involved in the release of solid substances from an apolar medium. Extrapolation of the results to the in vivo release is speculative, because as stated in the introduction, thein vivo release process was studied only in part and under conditions in many ways different from thein vivo situation. Investigations are in progress to study the spreading of suppositories in vivo and to establish the exact conditions in the rectum after administration of a suppository in order to be able to improve thein vitro simulation of thein vivo situation.
Unable to display preview. Download preview PDF.