Mechanisms of percutaneous absorption of tamoxifen by terpenes: eugenol, D-limonene and menthone.

The effect of chemical penetration enhancers (e.g., eugenol, d-limonene and menthone in combination with 50% ethanol) on the in vitro percutaneous absorption of tamoxifen through porcine epidermis has been investigated. The above enhancers significantly increased (p<0.05) the permeability coefficient of tamoxifen in comparison with the control (50% ethanol). Fourier transform infrared spectroscopy (FT-IR) was employed to investigate the biophysical changes in the stratum corneum (SC) lipids by the enhancer(s). FT-IR results showed that the treatment of the SC with enhancers did not produce a blue shift in the asymmetric and symmetric C-H stretching peak positions. However, all of the above enhancers showed a decrease in peak heights and areas for both asymmetric and symmetric C-H stretching absorbances in comparison with the untreated SC. A decrease in peak heights and areas is a measure of lipid extraction. Partitioning of tamoxifen to powdered SC from control and enhancer solutions was also determined. FT-IR and partitioning studies reveal that the enhancement in the permeability coefficient of tamoxifen by eugenol and d-limonene is due to lipid extraction and improvement in the partitioning of the drug to the SC. However, menthone enhanced the permeability of tamoxifen by increasing extraction of the SC lipids and not by improving the partitioning of the drug to the SC.