Influence of vehicles on the in vitro percutaneous absorption of piroxicam to optimise the formulation of patch tests in dermatology

The present study evaluated the influence of various vehicles on the in vitro percutaneous absorption of piroxicam across human skin under standard diffusion conditions to optimise the formulation of patch tests in dermatology. The transdermal permeation properties of piroxicam were evaluated from five vehicles (PEG 400, propylene glycol, transcutol P, petrolatum, and petrolatum + transcutol P 10%) using Franz diffusion cells. Piroxicam was applied as a saturated solution in vehicles to ensure equal thermodynamic activity of piroxicam in the vehicles. Concentrations of piroxicam were determined by high performance liquid chromatography in epidermis, dermis, and receptor liquid. The release of piroxicam from its vehicles and consequently its cutaneous absorption are influenced by the vehicle assayed and the solubility of piroxicam in each vehicle. The penetration of piroxicam through human skin was clearly enhanced by propylene glycol and petrolatum + transcutol P 10%, with cumulated amounts of piroxicam in the receptor fluid at 48 h of 116±32 and 159±28 μg/mg/cm² respectively, whereas petrolatum alone did not allow the diffusion of piroxicam. Additional experiments should be conducted in vivo to correlate the results obtained in vitro and to provide clinicians with a more reliable diagnostic test. Drug Dev. Res. 58:283–290, 2003. © 2003 Wiley‐Liss, Inc.