Quality by Design-Driven Development of Etoricoxib-Loaded Emulgel with Synergistic Penetration Enhancement: Optimization, Characterization, and Sustained Release Evaluation for Topical Anti-Inflammatory Therapy

AbstractChronic inflammatory conditions such as osteoarthritis and rheumatoid arthritis affect millionsworldwide, with oral nonsteroidal anti-inflammatory drugs remaining the mainstay oftreatment despite significant systemic adverse effects. Etoricoxib, a highly selectivecyclooxygenase-2 inhibitor, offers potent anti-inflammatory activity but is limited by pooraqueous solubility, extensive first-pass metabolism, and potential cardiovascular andgastrointestinal toxicities upon oral administration. To address these limitations, the presentstudy focused on the development, optimization, and comprehensive characterization of anetoricoxib-loaded emulgel for enhanced topical drug delivery. Preformulation studiesestablished oleic acid and Transcutol P as optimal vehicles based on solubility profiling, withetoricocib exhibiting a log P of 2.84 that falls within the favorable range for transdermalpermeation. A validated stability-indicating HPLC method was developed, and drug-excipientcompatibility was confirmed through differential scanning calorimetry and Fourier-transforminfrared spectroscopy. Formulation optimization was conducted using a three-factor, three-levelBox-Behnken design with oil concentration, surfactant mixture concentration, and gelling agentconcentration as independent variables, while cumulative drug release at 8 hours, viscosity, andspreadability served as critical quality attributes. The optimized formulation achieved adesirability value of 0.924 and comprised 12% oil, 12% surfactant mixture, and 0.8% carbomer934, with experimental values closely matching model predictions. The optimized emulgelexhibited nanosized droplets of 138 nanometers, a narrow polydispersity index of 0.168, and azeta potential of negative 31.4 millivolts, confirming excellent physical stability. Rheologicalcharacterization revealed pseudoplastic flow with thixotropic recovery, ideal for topicalapplication. In vitro drug release studies demonstrated sustained release over 24 hours with94.8% cumulative drug release, following anomalous non-Fickian transport kinetics asconfirmed by the Korsmeyer-Peppas model. Accelerated stability testing at 40 degrees Celsius and 75% relative humidity for 6 months confirmed formulation robustness with a predictedshelf-life of 24 months. Overall, this research establishes a scientifically robust, patient-friendlytopical delivery platform that enhances therapeutic efficacy while reducing systemic toxicity,offering a promising alternative for the management of localized inflammatory disorders.