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Therapeutic macromolecules including peptides, proteins, and nucleotide-based ones (such as antisense oligonucleotides and RNAs) have great potential as drug candidates. One drawback is that they typically need to be administered parenterally via subcutaneous, intramuscular or intravenous injections. Patients and healthcare professionals, however, generally prefer medicines that are taken orally. Absorption of therapeutic macromolecules after oral administration is unfortunately limited due to their instability in the gastrointestinal tract, as well as their poor permeability across the mucosa, owing to their large and hydrophilic nature.

Different formulation approaches can improve the absorption of macromolecules after oral administration. Permeation enhancers are the most studied technology for this purpose, and has resulted in two approved products. Yet despite many years of studying permeation enhancers, the bioavailability in clinical studies remains low and highly variable. Because of this, the use of permeation enhancers is currently limited to potent compounds with wide safety margins and long half-lives. Increasing the bioavailability and reducing variability thereof, would allow a wider range of drug candidates to be delivered using this formulation technology.

This thesis aims to improve the understanding of the low and variable absorption of solid dosage forms containing permeation enhancers. It includes studies on the absorption of different macromolecules co-delivered with the permeation enhancer sodium caprate (C10) in three pre-clinical models. To investigate the impact of intestinal C10 concentration, formulations with increasing C10 concentrations were administered to the upper small intestine of rats. C10 was rapidly absorbed and for the proteolytically stable macromolecules, a strong correlation between the C10 concentration and their bioavailability was observed. Furthermore, FITC-dextrans displayed an increase in both the initial rate and duration of absorption. In contrast, only the duration of increased absorption was prolonged for MEDI7219. Histological evaluation of the intestinal mucosa indicated that macromolecule absorption was correlated with erosion of the epithelium. On the basis of these results in rat, solid dosage forms designed to release C10 and peptide in high concentrations were studied in both pig and dog. A dosage form that achieved highly localized release showed promise in decreasing the absorptive variability of a model peptide.