The aim of current study was to develop an efficacious topical formulation of diclofenac diethylamine (DDA), for eventual use as a locally applied analgesic lotion. A series of lotions were prepared that incorporated 2% w/v DDA but a variable (1, 2, 3 or 4% v/v) concentration of oleic acid (permeation enhancer)-turpentine oil binary mixture (1:1 v/v). After measurements of each lotion's visual appearance, viscosity, spreadability, pH and long term stability, a diffusion cell method was employed to quantify DDA permeation from each lotion across both silicone membranes and rabbit skin. Subsequently, three distinct in vivo animal models were utilised to evaluate each lotion's induced anti-inflammatory, antinociception and irritancy effects. Lastly, a panel of human volunteers assessed the subjective sensory feel of each lotion as well as its potential for cutaneous irritancy following a brief application. Upon preparation, all four DDA-containing lotions (L1, L2, L3 and L4) appeared as clear, colourless, homogenous and aggregate-free solutions. All the lotions exhibited a pH of ∼6.2 with non-significant (p > 0.05) differences between each formulation (data not shown). Increasing the formulation's oleic acid concentration yielded a general trend of mild enhancement of DDA transport across silicone membrane and dramatic improvements of DDA flux through rabbit skin. Application of each of the DDA-containing formulations significantly reduced tissue inflammation in the rabbit model. It was determined that the DDA lotion containing 4% v/v oleic acid exhibited the best performance overall and that this specific formulation should be the basis for further clinical investigation.

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