By pairing insulin with a fat-soluble molecule and loading it into a self-emulsifying system, researchers achieved measurable oral insulin absorption in diabetic rats.
3.23% oral availabilityA measurable fraction of insulin survived the gut and lowered blood sugar when delivered in an optimized microemulsion — small but significant for oral peptide delivery
What the researchers found
A self-microemulsifying drug delivery system (SMEDDS) using hydrophobic ion pairing achieved oral insulin absorption in diabetic rats with pharmacological availabilities of 3.23% at 50 IU/kg and 2.13% at 100 IU/kg. The optimized formulation protected insulin from gastrointestinal enzyme degradation and kept the majority of insulin within oil droplets during release. The formulation used an insulin complex with sodium n-octadecyl sulfate loaded into an optimized microemulsion with droplet sizes of 115.2 nm.
Why it matters
Insulin injections are the daily burden millions of diabetics live with. If insulin could be taken as a pill, it would transform diabetes management. This study demonstrates a formulation strategy that achieves measurable oral insulin absorption — small percentages, but proof that the approach works and can be optimized further.
How the study worked
Researchers first complexed insulin with sodium n-octadecyl sulfate (SOS) to make it more fat-soluble. They then used a D-optimal mixture design — a statistical optimization method — to create the best SMEDDS formulation from three components: Capmul MCM (9.31%), Labrasol (49.77%), and Tetraglycol (40.92%). The formulation was characterized for droplet size, insulin stability, and insulin leakage. Finally, it was administered orally to diabetic rats and blood glucose responses were measured to calculate pharmacological availability.
Who was studied
Diabetic rats (streptozotocin-induced diabetes model)
What this study cannot tell us
The study was conducted in diabetic rats, not humans, and oral bioavailability was low (2–3%). Rat gastrointestinal physiology differs from humans in ways that affect oral absorption. Long-term stability of the formulation was not assessed. The study did not evaluate repeated dosing or potential toxicity of the formulation components.
How to read the evidence
This is a preclinical formulation study in rats. While it demonstrates proof of concept, no human data exists, and the bioavailability achieved is still far from clinical utility.
When this study was published
Published in 2022, this represents recent work in the oral peptide delivery field. The SMEDDS approach continues to be explored alongside competing technologies for oral insulin.
The bigger picture
The quest for oral insulin has been going on for decades, with most approaches failing because too little survives the gut. This study contributes one more strategy — hydrophobic ion pairing plus SMEDDS — that achieves measurable absorption. While 2–3% isn't enough for a commercial product, the approach could be combined with other strategies (absorption enhancers, enteric coatings) to push availability higher.
Questions still open
- Can the 2–3% pharmacological availability be improved enough to create a commercially viable oral insulin product?
- How would this formulation perform in humans, where gut transit time and enzyme exposure differ from rats?
- Could this SMEDDS platform be applied to other peptide drugs beyond insulin?
Common questions
How does this make oral insulin possible?
Is 3% bioavailability good enough for oral insulin?
Read the original research
Enhanced oral absorption of insulin: hydrophobic ion pairing and a self-microemulsifying drug delivery system using a D-optimal mixture design.
Drug delivery, 29(1), 2831-2845
Citation
Goo, Yoon Tae; Lee, Sangkil; Choi, Ji Yeh; Kim, Min Song; Sin, Gi Hyeong; Hong, Sun Ho; Kim, Chang Hyun; Song, Seh Hyon; Choi, Young Wook. (2022). Enhanced oral absorption of insulin: hydrophobic ion pairing and a self-microemulsifying drug delivery system using a D-optimal mixture design.. Drug delivery, 29(1), 2831-2845. https://doi.org/10.1080/10717544.2022.2118399