FORMULATION, OPTIMIZATION AND ESTIMATION OF CELECOXIB TOPICAL EMULGEL

Abstract

Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, is widely used for chronic inflammatory disorders such as rheumatoid arthritis and osteoarthritis. However, its clinical utility via oral administration is restricted by negligible aqueous solubility, extensive first-pass hepatic metabolism by CYP2C9, and adverse gastrointestinal, renal, and cardiovascular effects. The objective of the present investigation was to formulate, optimize, and characterize a stable celecoxib topical emulgel to achieve sustained localized anti-inflammatory action, enhance cutaneous permeability, and minimize systemic exposure. A 23 factorial design was implemented to optimize the formulation parameters by evaluating three independent variables: gelling agent type (Carbopol 934 vs. HPMC), concentration of liquid paraffin (5.0% vs. 7.5% w/w), and emulsifier blend concentration (Tween 20 / Span 20 at 1.5% vs. 2.5% w/w). Preformulation screening included organoleptic testing, UV spectrophotometric calibration, equilibrium solubility profiling across multiple solvents, and forced degradation studies under stress conditions. Drug-excipient compatibility was investigated using Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Formulations (F1–F8) were evaluated for physical appearance, pH, rheological behavior, spreadability, drug content uniformity, in vitro drug release via vertical Franz diffusion cells across synthetic dialysis membranes, mathematical release kinetics, ex-vivo permeation through excised porcine skin, and accelerated stability according to ICH Q1A(R2) guidelines. Preformulation confirmed drug purity with a melting endotherm at 161.8 °C and λmax of 252 nm. FTIR and DSC studies demonstrated the preservation of characteristic functional peaks (3336 cm−1 N–H stretch, 1348 cm−1 SO2 stretch) without chemical degradation. All eight batches exhibited skin-compatible pH (6.18 ± 0.04 to 6.42 ± 0.04), viscosity ranging between 21,450 ± 120 and 29,580 ± 180 cP, spreadability between 17.6 ± 0.30 and 24.6 ± 0.42 g·cm/s, and drug content between 97.42 ± 0.64% and 99.48 ± 0.29%. Formulation F6 (2.5% HPMC, 5% liquid paraffin, 2.5% surfactant) was identified as the optimal batch, demonstrating superior spreadability (22.4 ± 0.34 g·cm/s), desirable viscosity (24,120 ± 145 cP), and highest sustained in vitro cumulative drug release of 93.2 ± 1.2% over 36 hours compared to the standard formulation (45%). Release kinetics best fitted the Higuchi diffusion model (R2=0.996), confirming diffusion-controlled drug release. Ex-vivo permeation revealed a cumulative transdermal delivery of 75.6 ± 1.9% (4267±107 μg/cm2) and cutaneous retention of 12.8 ± 1.1%. Accelerated stability studies (40±2 ∘C / 75±5% RH for 3 months) showed no significant degradation or physicochemical alterations (p>0.05). The developed celecoxib emulgel (F6) provides controlled release, high skin permeation, and excellent physical stability, making it an effective alternative to conventional oral celecoxib delivery.