Topical delivery of diclofenac into and across equine skin from a novel liquid diclofenac epolamine formulation

The aim was to investigate diclofenac delivery into and across equine skin in vitro using Franz diffusion cells from a novel diclofenac epolamine (DIC-EP; 1.3%) formulation and to compare the results to those of Surpass (R) (1% diclofenac sodium liposomal cream) and a 1% aqueous solution of diclofenac sodium. Skin was harvested from the lower legs of Freiberger geldings immediately after slaughter and sliced to a thickness of similar to 2 mm. Skin samples were divided into two groups [Group 1: 1 year old (n = 2) and Group 2: 6-8 years old (n = 3)]. Cumulative permeation of diclofenac in Groups 1 and 2 after 24 h using diclofenac sodium solution was 1.91 +/- 0.27 and 1.76 +/- 0.34 mu g/cm(2), respectively. The values for Surpass (R) and DIC-EP were 3.2 +/- 0.8/3.3 +/- 0.7 mu g/cm(2) and 230 +/- 59/89.2 +/- 32.5 mu g/cm(2), respectively. Thus, diclofenac permeation from DIC-EP was significantly greater and appeared to show an age-dependent effect. Mathematical modelling showed that the DICEP formulation significantly increased diclofenac partitioning into the skin and a linear correlation was observed between steady-state flux and the partition parameter. Greater skin deposition of diclofenac was also observed with DICEP. These preliminary results suggest that the DIC-EP formulation may be effective in treating inflammatory conditions in horses.