DYNAMICS OF THE SKIN BLOOD-FLOW RESPONSE TO HISTAMINE - COMPARISON OFTHE EFFECTS OF CETIRIZINE AND LORATADINE ON THE SKIN-RESPONSE TO A HISTAMINE DRY PRICK TEST MONITORED WITH LASER-DOPPLER FLOWMETRY

In previous studies, we noticed that intradermal injection of histamin e solutions might significantly complicate the interpretation of clini cal data and of laser-Doppler flowmetry recordings (LDF). Therefore, w e used the histamine dry skin prick test (HPT) for pharmacological stu dies. In this study, LDF monitoring of the physiological skin response to histamine was made in a randomized, placebo-controlled, double-bli nd study comparing the in vivo anti-H-1 activity of cetirizine (10 mg) or loratadine (10 mg), 6 h after a single oral intake. As compared wi th responses recorded after intake of placebo, LDF readings performed at HPT sites (increase in LDF signal) and at 1 cm from HPT (reduction of LDF signal) conclusively illustrate the stable and almost complete blockade of H-1 receptors by cetirizine. In vivo effects obtained with loratadine were considered weaker because (1) there was no significan t influence of loratadine on the blood flow recorded at HPT sites, (2) a significant reduction at 1 cm from HPT sites was observed only afte r a lag phase (greater-than-or-equal-to 10 min) and (3) there were sig nificantly higher skin perfusion levels at 1 cm from HPT sites between 6 and 10 min after the test under loratadine as compared with cetiriz ine. Hence, multipoint probing with LDF over time appears as a sensiti ve method for discriminating response profiles between two anti-H-1 ag ents. Furthermore, this is the first time that anti-H-1-related change s of the dynamics of expansion of the flare response have been demonst rated.