Rectal and Vaginal Absorption of Peptides and Proteins

Abstract

Peptide/protein drugs are increasingly becoming a very important class of therapeutic agents as a result of our gaining more understanding of their role in physiology and pathology as well as the rapid advances in the field of biotechnology/genetic engineering. These drugs are generally not suitable for oral administration, since they are poorly absorbed and easily degraded by proteolytic enzymes in the gastrointestinal tract (Lee and Yamamoto, 1990). For systemic delivery of peptide and protein drugs, parenteral administration is currently required in order to achieve their therapeutic activities. However, these administration routes are poorly accepted by patients and may cause an allergic reaction. Thus, alternative routes such as nasal (Hirai et al., 1981a), buccal (Ishida et al., 1981), rectal (Nishihata et al., 1983), vaginal (Okada et al., 1982), conjunctival (Yamamoto et al., 1989), and transdermal (Liu et al., 1988) are being investigated for peptide and protein delivery. Among these routes, rectal and vaginal are potentially important routes for peptide administration, although they are poorly accepted in several countries. In contrast to the oral route, the rectal delivery of peptide/protein drugs provides the advantage of greater systemic bioavailability, especially with the coadministration of adjuvants. Additional advantage is the avoidance of first-pass elimination (de Boer et al., 1980). On the other hand, in the vaginal membrane, the predominant transport of lipophilic substances takes place by partition and diffusion through the transcellular lipoidal passage.