Transethosomal diflunisal gel: Physicochemical characterization, skin permeation, and antinociceptive activity in mice

Purpose: Diflunisal is a nonsteroidal anti-inflammatory drug whose topical delivery is constrained by low aqueous solubility and the stratum corneum barrier. This study characterized a diflunisal-loaded transethosomal gel and evaluated its ex vivo skin permeation, antinociceptive activity, and short-term physicochemical changes during storage.Method: Diflunisal-loaded transethosomal gel was evaluated for physicochemical properties, ex vivo skin permeation, antinociceptive activity in Swiss mice (n = 8/group), and physicochemical changes during 12 weeks of storage. Permeation profiles were analyzed using a linear mixed-effects model, whereas flux and antinociceptive data were analyzed using one-way analysis of variance.Results: Ex vivo permeation across excised mice skin demonstrated superior delivery from the transethosomal gel, with a cumulative permeation (Q) of 279.789 ± 6.351 μg/cm² compared with 177.688 ± 9.173 μg/cm² for the non-transethosomal gel. In vivo evaluation using the formalin-induced nociception model demonstrated significant antinociceptive activity in both phases. Formalin-evoked licking/biting times were lower in both diflunisal-treated groups than in the untreated formalin group. No statistically significant difference was observed between the oral and topically treated groups in this small experiment; this does not establish equivalence between the routes. Storage at 40 ± 2 °C produced greater changes in color, pH, viscosity, and measured drug content than storage at 30 ± 2 °C.Conclusion: The diflunisal-loaded transethosomal gel enhanced ex vivo skin permeation and was associated with reduced formalin-evoked nociceptive behavior. These findings support further investigation of the formulation as a topical delivery system for diflunisal. Further pharmacokinetic, safety, vehicle-controlled, and disease-specific studies are required.