Validation of a microdialysis-gas chromatographic-mass spectrometric method to assess 8-methoxypsoralen in psoriatic patient dermis.

8-Methoxypsoralen (8-MOP) is currently used in PUVA therapy (psoralen+UVA) to treat dermatological diseases such as psoriasis, vitiligo and atopic dermatitis. The aim of this work was to validate a method for collecting 8-MOP from patient dermis by a non invasive technique, microdialysis, and then to assess this molecule by gas chromatography-mass spectrometry (GC-MS). 5-Methoxypsoralen (5-MOP) was used as an internal standard. The calibration curve demonstrated a linear relationship between the peak areas of 8-MOP and 5-MOP over a wide range of 8-MOP concentrations (0.9-100 ng/ml). Within- and between-run precisions were measured, using four different 8-MOP concentrations, which varied from 98.0 to 102.0% and from 98.5 to 101.8%, respectively. The limits of detection and quantification were 0.29 and 0.52 ng/ml, respectively. The method was validated and then applied to determine the pharmacokinetic of 8-MOP in ten psoriatic patient dermis, after oral intake of this drug. The results demonstrated that the association of microdialysis with the GC-MS method was an efficient procedure to collect and assess 8-MOP in human dermis, in vivo.