Central composite design-based optimization, fabrication, and pharmacodynamic assessment of sulfasalazine-loaded lipoidal nanoparticle-based hydrogel for the management of rheumatoid arthritis.

Rheumatoid arthritis is a progressive, chronic, immunological, and inflammatory disorder that is distinguished by joint inflammation, joint tenderness, and synovial joint destruction. The study aimed to fabricate sulfasalazine-loaded solid lipid nanoparticle (SLN)-based gels for rheumatoid arthritis management. The SLNs were fabricated with the melt emulsification technique by employing central composite design (CCD) for SLNs optimization. The optimized formulation of SLNs (FF-1) showed particle size and drug entrapment efficiency of 117.25 nm ± 1.67 and 94.05% ± 1.05, respectively. To scrutinize the outcome of the independent variable on responses; model graphs and the polynomial equation obtained from the Design-Expert were used. The surface morphology studies of SLNs revealed a smooth surface with a slightly asymmetric shape. In vitro drug release of the optimized formulation (FF1) had shown a maximum release of up to ~ 91.89% ± 2.12 over 24 h. The optimized FF1 formulation was subsequently gelled using 1% w/v Carbopol 934 and subjected to ex vivo permeation that displayed 8.01 mg/cm 2  ± 0.24 and 7.49 mg/cm 2  ± 0.86 amount of drug permeated up to 24 h and 10 h from SLNs gel and plain gel, respectively. In vivo studies manifested a considerable reduction in the paw thickness (*p < 0.0001) and an arthritic score (*p < 0.0001) of the sulfasalazine SLN gel as compared to plain gel. Further, pro-inflammatory cytokines, viz. TNF-α, IL-1, and IL-6 levels, were significantly inhibited (p < 0.0001) by sulfasalazine SLN-based gel that exhibited substantial anti-inflammatory effects. In conclusion, sulfasalazine-loaded SLN-based gel showed sustained release of drug for up to 24 h and can be considered suitable as a topical application for rheumatoid arthritis management.