RELEASE OF DRUGS FROM FATTY SUPPOSITORY BASES .1. RELEASE MECHANISM

A model for drug release from fatty suppository bases is presented that explains in vitro measurements on drugs with various physicochemical characteristics, such as paracetamol (slowly dissolving in water) sodium salicylate (rapidly dissolving in water) and salicylic acid (soluble in lipid). The in vitro results are compared with in vivo experiments on rectal absorption in man. Results indicated that for suspensions of all the drugs investigated, dissolution takes place at the interface between the suppository base and the surrounding fluid. The release process therefore includes a flow of particles in the suppository base into the direction of the interface and a flow of solute away from the interface. Either of these flows may be rate limiting dependent on the water solubility of the drug, and may determine the effect of concentration and particle size on release rate. © 1979.