Hydrophobic ion pairing with THA surfactant enabled oral exenatide delivery with 28% bioavailability in rats — a breakthrough for injectable peptide drugs.
28% oral bioavailabilityfor exenatide using hydrophobic ion pairing with THA surfactant in lipid nanocarriers — vs near-zero for unformulated peptide
What the researchers found
Exenatide is a peptide drug given by injection because it is destroyed in the gut and cannot cross the intestinal wall. Hydrophobic ion pairing (HIP) makes peptides lipophilic by pairing them with surfactant counterions.
Two surfactant types were tested: cationic THA (tetraheptylammonium bromide) and anionic DOC (sodium docusate). Both formed stable complexes with exenatide.
Exenatide-THA was more lipophilic (log D of 2.29 in simulated intestinal fluid vs 1.2 for exenatide-DOC). When loaded into lipid nanocarriers (41% Capmul MCM, 15% Captex 355, 40% Cremophor RH, 4% propylene glycol), the THA formulation showed:
- 10-fold enhancement in intestinal apparent membrane permeability vs free exenatide
- 28.0% ± 5.2% relative oral bioavailability in healthy rats
The DOC formulation achieved 3-fold permeability enhancement and 16.3% ± 6.6% bioavailability.
Neither formulation caused significant hemolytic activity at 0.25% concentration, indicating safety for oral use.
Why it matters
GLP-1 drugs like exenatide, semaglutide, and liraglutide are revolutionizing diabetes and obesity treatment, but most require injection. Oral delivery would dramatically improve patient compliance. Achieving 28% oral bioavailability for a peptide drug is remarkable; oral semaglutide (Rybelsus) has only about 1% bioavailability.
The numbers in context
28% oral bioavailability (THA); 16% (DOC); 10x permeability enhancement; non-hemolytic; log D 2.29
How the study worked
Pharmaceutical formulation study. Hydrophobic ion pairs prepared with THA and DOC surfactants. Lipophilicity measured by partition coefficients. Nanocarriers characterized for hemolytic activity. Intestinal permeability tested using standard membrane models. Oral bioavailability measured in healthy rats compared to subcutaneous injection.
Who was studied
Healthy rats (oral pharmacokinetic study)
What this study cannot tell us
Tested in healthy rats, not diabetic animals or humans. Rat oral bioavailability does not always translate to human bioavailability. The lipid nanocarrier composition may not be optimized yet. Long-term stability of the ion-paired formulation was not assessed. The 28% bioavailability is relative to subcutaneous injection; absolute absorption may be lower.
How to read the evidence
Preliminary evidence from rat pharmacokinetic studies. Promising numbers but human oral bioavailability often differs significantly from rats.
When this study was published
Published in 2020. Oral peptide delivery technology continues to advance alongside approved oral semaglutide.
The bigger picture
Most GLP-1 drugs require injection, limiting patient adoption. Oral semaglutide (Rybelsus) was the first oral GLP-1, using a different technology. This hydrophobic ion pairing approach could enable oral versions of other injectable peptide drugs, expanding access to these important medications.
Questions still open
- Would 28% bioavailability in rats translate to clinically useful levels in humans?
- Can this formulation maintain stability during storage?
- Could this approach work for other injectable peptide drugs like insulin?
Common questions
Why is oral delivery of peptide drugs so difficult?
Is 28% bioavailability good?
Read the original research
Hydrophobic ion pairing of a GLP-1 analogue for incorporating into lipid nanocarriers designed for oral delivery.
European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V, 152, 10-17
Citation
Ismail, Ruba; Phan, Thi Nhu Quynh; Laffleur, Flavia; Csóka, Ildikó; Bernkop-Schnürch, Andreas. (2020). Hydrophobic ion pairing of a GLP-1 analogue for incorporating into lipid nanocarriers designed for oral delivery.. European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V, 152, 10-17. https://doi.org/10.1016/j.ejpb.2020.04.025