Combined Effect of Oleic Acid and Propylene Glycol on the Percutaneous Penetration of Tenoxicam and Its Retention in the Skin

The influence of oleic acid (OA) on the in vitro percutaneous absorption of tenoxicam (TEN) and its combined effect with propylene glycol (PG) was studied using Franz-type diffusion cells. Furthermore, at defined concentrations of OA, complexes of the drug with cyclodextrins (MbetaCD and gammaCD) were added because their combined use may be an interesting approach to raise TEN flux. In addition, the amount of TEN retained in the skin after topical administration of several formulations was determined. It was found that OA content markedly increased TEN absorption when compared to the control gel; the highest drug flux was obtained by 15% of OA. The absorption rate of TEN increased in parallel with increasing OA concentration, due to the alteration of the stratum corneum caused by this enhancer. Moreover, the action of OA is likely to be strongly dependent on the vehicle used since drug penetration tended to increase with increasing PG content in the vehicle, especially at the high OA concentrations. Contrary to our expectations, addition of CD complexes did not produce a significant further enhancement. Skin pretreatment with OA, independently of the vehicle used to dissolve the fatty acid, dramatically improved TEN percutaneous penetration. The amount of TEN retained in the skin was related to the flux values obtained with each formulation.