Psoralen-ultraviolet A-induced erythema: sensitivity correlates with the concentrations of psoralen in suction blister fluid

Since the advent of psoralen-ultraviolet A (PUVA) therapy, the Value of pla sma 8-methoxypsoralen (8-MOP) concentrations to predict PUVA-induced erythe ma has been widely investigated. Plasma 8-MOP concentrations have not been proportional to, and cannot alone predict, the degree of PUVA-induced eryth ema. We assumed that PUVA-induced erythema was related more closely to psor alen concentrations in the skin tissue rather than those within blood vesse ls. This study was designed to investigate the correlations between the 8-M OP concentrations in suction blister fluid (SBP) and in plasma, with the de gree of PUVA-induced erythema. 8-MOP concentrations in plasma and SBF were measured in 15 vitiligo patients and 11 volunteers. Blood and SBF samples w ere collected 2 h after taking 8-MOP, and 8-MOP concentrations in plasma an d SBF were quantified using reverse-phase high-performance liquid chromatog raphy. Eleven volunteers were phototested using a series of doses of ultrav iolet A at the time of sampling. The erythema responses were estimated visu ally to determine the minimal phototoxic dose (MPD). SBF 8-MOP concentratio ns showed a weak positive correlation with plasma 8-MOP concentrations, whi ch means that we could not predict the exact SBF 8-MOP concentrations using the plasma 8-MOP concentrations. The MPD showed a better correlation with the log of the SBF 8-MOP concentration than with that of the plasma 8-MOP c oncentration. These results show that plasma 8-MOP concentration cannot rep resent the exact SBF 8-MOP concentration, and that SBF 8-MOP concentrations , which are representative of the skin tissue 8-MOP level. are more closely related to the erythemal sensitivity during PUVA therapy.