Development of Topical Gel of Capsaicin Loaded Solid Lipid Nanoparticles (SLNs): in vitro and in vivo Evaluation

Purpose: The aim of this study was to evaluate and compare the in vitro and in vivo topical potential of solid lipid nanoparticles (SLNs) gel for capsaicin. Methods: SLNs were prepared by high shear homogenization and ultrasonication using capsaicin. Then SLNs gel was formulated by hydration method using carbopol 940. Results: The mean particle size, width of distribution, zeta potential and entrapment efficiency of SLNs were 100 nm, 0.374, -48.36 mV and 63.5 ± 2.9 respectively. The scanning electron microscopy (SEM) image revealed that capsaicin in SLNs was in amorphous state. Capsaicin release was prolonged to 14 hr with encapsulation (94.3±3.8%). Drug loaded SLNs showed transdermal flux of 30.43±2.5 μg/cm2/h indicating synergistic effects of encapsulation of capsaicin in SLNs. Permeation of optimized formulation was found to be about 1.6 fold times higher than plain drug. Drug loaded SLNs showed 51% remission in inflammation at the end of study (28th day). In the paw edema test, SLN-5 showed the best permeation and effectiveness. The results of the present study demonstrated SLN-5 gel formulation possesses great potential for enhanced skin accumulation, prolonging drug release and improving the site specificity of capsaicin Conclusion: SLNs containing capsaicin could be prepared successfully by using an ultrasonic technique, which will not only sustain the release of drug but also increase permeation of drug to dermal layer of skin. The in vitro and in vivo studies showed that SLN5 formulation prepared without organic solvent could be a new, alternative dosage form for effective therapy.