A nanoemulsion based transdermal delivery of insulin: Formulation development, optimization, in-vitro permeation across Strat-M® membrane and its pharmacokinetic/pharmacodynamic evaluation

Peptides and proteins are mainly delivered through the parenteral route which is painful and reduces patient compliance. The aim was to explore the feasibility of using nanoemulsion as an alternative carrier for the transdermal delivery of insulin. For this purpose, pseudoternary phase diagram was constructed to determine the exact ratio of nanoemulsion components. A Simplex lattice design was used to formulate nanoemulsion comprising of oleic acid, tween 80, isopropyl alcohol, and water as independent variables and droplet size, entrapment ratio, and flux as responses. Particle size distribution was determined through DLS and SEM. The gradient-HPLC method for the quantification of insulin was developed and validated. The in vitro permeation was carried out using Strat-M® membrane. Circular dichroism (CD), native gel electrophoresis, storage stability at 4 °C, skin irritation, pharmacokinetics, and pharmacodynamic study of optimized nanoemulsion were also performed. Optimized formulation was based on the small droplet size (41.05 ± 8 nm), maximum entrapment ratio (93.08%), and higher flux of (1.75 μg/cm 2 /h). The developed chromatographic method detected insulin in the range of 0.5–2.4 μg/mL. The CD spectra revealed minor changes in the secondary structure of insulin due to the entrapment in the micelles of nanoemulsion. The optimized nanoemulsion formulation was stable for three months. The PK/PD analysis indicated the slow absorption of insulin from the nanoemulsion as compared to SC injection in Albino Wister rats, resulting in delayed and consistent response having relative bioavailability of 244.5%. The results indicate that this system may be a promising vehicle for transdermal insulin delivery. • A Simplex lattice design was used to formulate nanoemulsion as an alternative carrier for the transdermal delivery of insulin. • Particle size distribution was determined through DLS and SEM. • The gradient-HPLC method for quantification of insulin was developed and validated. • The in vitro release and permeation was carried out using Strat-M® membrane. • Subcutaneous injection and transdermal nanoemulsion administration of insulin in Albino Wister rats for PK/PD evaluation. • Circular dichroism, native gel electrophoresis and storage stability of optimized nanoemulsion at 4 °C was also performed. • The optimized nanoemulsion formulation was stable for three months. The results indicate that this system may be a promising vehicle for transdermal insulin delivery.