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Abstract The goal of the current research was to investigate the release of diclofenac sodium and leflunomide, poorly water-soluble drugs from microemulsion gel formulations in vitro. This study is providing a new type of drug delivery that combines the advantages of a microemulsion with transdermal administration and combination therapy for rheumatoid disease. The combination therapy, immunomodulatory (leflunomide) and NSAIDs (diclofenac sodi um) were formulated, optimized and evaluated after loaded into a micro-emulsionbased gel for active rheumatoid arthritis (RA). Various surfactants and cosurfactants were screened for their ability to emulsify the selected oily phase. The pseudoternary diagrams were constructed to identify the area of microemulsion existence. A microemulsion (ME) was prepared using isopropyl myristate (IPM) as oil phase, tween 80 as surfactant and 1- pentanol as co-surfactant were assessed for droplet size, polydispersability index, zeta potential. The average droplet size and zeta potential values for selected formulation were 31.54±5.37 nm and -7.14±2.91 respectively. Optimized microemulsion systems were formulated into gel form to enhancing the viscosity, carbopol was used to form a MEbased gel then the ME gel evaluated for pH, spreadability, viscosity, drug content, differential scanning calorimetry (DSC), Fourier transform infrared spectra analysis (FTIR) and in vitro drug release using dialysis bag. For selected ME gel formulations, in vitro release has been studied and F2C formula showed appropriate cumulative drug release (77.36% for leflunomide and 89.90% for diclofenac sodium) after 24 hr. The in vitro result suggested that ME systems are powerful topical vehicles for enhanced penetration of leflunomide and diclofenac sodium. A 28-day antiarthritic evaluation (body weight, paw edema, haematological parameters and histopathology) on carrageenan-induced arthritic rat model after topical application of microemulsion-based combination therapy gel in rats showed significant reversal of arthritic symptoms. |