Comparison of skin permeability for three diclofenac topical formulations: an in vitro study.

Diclofenac is a hydrophilic non-steroidal anti-inflammatory drug (NSAID) widely used in humans and animals. There are limited published studies evaluating diclofenac's skin permeation following topical administration. The aim of our study was to evaluate and compare the in vitro permeation of three different diclofenac-containing formulations (patch, gel, solution) over 24 hours. These formulations were applied (n = 6 per formulation) to pig skin sandwiched between the two chambers in a static Franz diffusion cell and aliquots from the receptor medium were sampled at pre-defined time points. An HPLC method with UV detection was developed and validated with the aim of characterizing the transepidermal penetration in the in vitro system. Using this assay to determine the permeation parameters, results at 24 hours showed that the Flector patch released the highest drug amount (54.6%), whereas a lower drug amount was delivered with the Voltaren Emulgel (38.2%) and the solution (34.4%). The commercial gel showed the highest flux (39.9 +/- 0.9 microg/cm2/h) and the shortest lag-time (1.97 +/- 0.02 h). Based on these in vitro results using pig skin, the transdermal patch resulted in a long-lasting controlled release of diclofenac, while the gel had the shortest lag-time.