BIOPHARMACEUTICAL STUDIES OF FATTY SUSPENSION SUPPOSITORIES .2. INFLUENCE OF PARTICLE-SIZE AND CONCENTRATION ON INVITRO RELEASE OF READILY WATER-SOLUBLE COMPOUNDS

The influence of particle size and concentration of lithium sulphate, as a readily water-soluble compound, on the in vitro release rate from fatty suppository vehicles is described. The results show a good correlation with the apparent viscosity of the suspension suppositories at 37°C. This indicates that the release may be described by a three-step model, i.e. transport of particles to the vehicle/water interface, transport through that interface, and finally dissolution. In the case of readily water-soluble compounds the first step, i.e. sedimentation, acts as rate-limiting. Thus small particles are released at a lower rate than larger particles. © 1979.