Suppositories formulation and drug release

This paper is concentrated on those suppositories where the drug substance is in suspension in a fatty vehicle. The drug release from such a dosage form can be divided in five stages, namely: melting of the suppository; spreading of the melted mass; sedimentation of the drug particles; passage of the solid particles through the oil/water interface; dissolution of the drug particles in the rectal aqueous fluid. The different factors involved in each stage are briefly reviewed for a better understanding of the influence of the formulation parameters on the drug release from fatty suppositories. A special attention is paid on the possible use of drug-PVP coevaporates to facilitate the passage through the oil/water interface and/or the dissolution in the rectal aqueous fluid when one or both of these processes have been identified as being the limiting steps of the drug release. Finally, the most recent works on the rectal absorption promoter such as enamines, sodium salicylate and related compounds, surfactants and mixed micelles are summarized.