Oral drug delivery is a preferred route because of good patient compliance. However, most peptide/
protein drugs are delivered via parenteral routes because of the absorption barriers in the gastrointestinal (GI)
tract such as enzymatic degradation by proteases and low permeability acrossthe biological membranes. To overcome
these barriers, different formulation strategies for oral delivery of biomacromolecules have been proposed,
including lipid based formulations and polymer-based particulate drug delivery systems (DDS). The aim of this
review is to summarize the existing knowledge about oral delivery of peptide/protein drugs and to provide an
overview of formulationand characterization strategies. For a better understanding of the challenges in oral delivery
of peptide/protein drugs, the composition of GI fluids and the digestion processes of different kinds of excipients
in the GI tract are summarized. Additionally, the paper provides an overview of recent studies on characterization of solid drug carriers
for peptide/protein drugs, drug distribution in particles, drug release and stability in simulated GI fluids, as well as the absorption of
peptide/protein drugs in cell-based models. The use of biorelevant media when applicable can increase the knowledge about the quality
of DDS for oral protein delivery. Hopefully, the knowledge provided in this review will aid the establishment of improved biorelevant
models capable of forecasting the performance of particulate DDS for oral peptide/protein delivery.
Keywords: Oral drug delivery, peptide/protein drugs, particulate delivery systems, solid lipid particles, drug release mechanism, stability,
lipolysis, in vitro methods.
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