A Fat-Based Formulation Gets Insulin Through the Gut in Diabetic Rats

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.

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.

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.

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.

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.