The effect of cetirizine and loratadine on codeine-induced histamine release in human skin in vivo assessed by cutaneous microdialysis

Objective and Design: To determine whether or not cetirizine and loratadine inhibit codeine- induced histamine release in human skin in vivo, we conducted a placebo-controlled double-blind trial in which histamine release was assessed by dermal microdiaysis. Subjects: A group of ten normal volunteers were studied, each subject visiting the laboratory on three occasions with intervals of at least 2 weeks between visits. Treatment: Cetirizine, loratadine (both 10 mg) or placebo was given orally 4 h before provocation of weal and flare responses in the skin by intradermal injection of 25 mu l of 3 or 10 mg/ml codeine 1 min from the centre of individual 216 mu m diameter microdialysis fibres inserted in the dermis. Methods: Dialysate was collected at 2 min intervals for 4 min before and 20 min after codeine injection and histamine assayed spectrofluorometrically. Weal and flare responses to codeine were assessed in the opposite arm. Results: Histamine concentrations in the microdialysis fibre outflow with 3 and 10 mg/ml codeine were maximal at 2 - 4 min when 910 +/- 156 and 1194 +/- 304 nM respectively were found in the placebo group. Cetirizine and loratadine did not modify either the kinetics or total histamine release while significantly (p < 0.01) inhibiting weal and flare responses. Conclusions: Neither cetirizine nor loratadine inhibited codeine-induced histamine release or modified the time course of its release in human skill in vivo when given in clinically used doses which are sufficient to significantly reduce weal and Rare responses.