(D) Routes of delivery: Case studies: (4) Rate-controlled rectal peptide drug absorption enhancement

The potentials and limitations of rectal peptide drug delivery as an alternative to parenteral administration are discussed. Several absorption enhancers have been shown to increase considerably the systemic availability of peptide drugs on rectal administration, which may vary with the rate of delivery of enhancer and peptide. It is emphasized that the concentration-effect relationship of enhancers should be investigated in terms of their influence on area under the plasma concentration-time curve of the peptide drug. Theoretical simulation experiments were performed to illustrate this. Furthermore, it is stressed that safety evaluation of enhancers in terms of causing potential mucosal damage should be given more attention.