FORMULATION OPTIMIZATION AND IN VITRO EVALUATION OF NLCS FOR TOPICAL DELIVERY OF ANDROGRAPHOLIDE AND THIOCOLCHICOSIDE

Nanostructured lipid carriers (NLCs) are advanced lipid-based nanocarriers that offer significant advantages for topical drug delivery, including improved drug loading, enhanced stability, controlled release, and better skin penetration. The present study focuses on the design, formulation optimization, and in vitro evaluation of nanostructured lipid carriers for topical delivery of a combination of andrographolide and thiocolchicoside using a Box–Behnken design (BBD) approach. Andrographolide, a bioactive diterpenoid with anti-inflammatory and antioxidant properties, and thiocolchicoside, a muscle relaxant, were selected to achieve a synergistic therapeutic effect. NLCs were prepared using an appropriate lipid blend consisting of solid and liquid lipids along with suitable surfactants. A three-factor, three-level Box–Behnken design was employed to optimize formulation variables, with particle size and entrapment efficiency considered as critical responses. Design-Expert® software was used to evaluate the effect of independent variables and to predict the optimized formulation. The optimized NLC formulation exhibited nanoscale particle size, high entrapment efficiency, and acceptable zeta potential, indicating good physical stability. The optimized NLCs were further characterized for drug content, in vitro drug release, and stability studies. In vitro release studies demonstrated a sustained and controlled release pattern of both drugs, suggesting improved topical performance. Stability studies confirmed that the formulation remained stable under accelerated storage conditions. Overall, the results indicate that the developed NLC-based topical formulation is a promising carrier system for the effective delivery of andrographolide and thiocolchicoside, with potential applications in the management of inflammatory and musculoskeletal conditions.