CONSISTENCY OF THE EFFICACY OF CETIRIZINE AND EBASTINE ON SKIN REACTIVITY

Background: At therapeutic dosage, cetirizine and ebastine induce sign ificant inhibition of skin reactivity to histamine. The consistency of their efficacy, that is, efficacy with the least interindividual vari ability among subjects, has not been carefully assessed, however. Obje ctive: To compare the consistency and efficacy of these antihistamines on skin reactivity. Methods: Twenty-four healthy volunteers participa ted in a randomized double-blind crossover study. The areas of wheals and flares induced by increasing (0, 5, 10, 50, 100, 200, and 300 mg/m L) histamine concentrations, administered by prick tests, were measure d before and four hours after intake of 10 mg of each antihistamine, a llowing concentration-response curves to be established. The threshold histamine concentrations inducing wheal areas of 3 mm2 (positivity) w ere calculated by interpolation. The coefficient of variation (SD/mean %) was used to evaluate the consistency of the response. Results: Pre treatment concentration-response curves were similar, and threshold co ncentrations identical (0.29 mg/mL and 0.34 mg/mL for cetirizine and e bastine, respectively). For both, curves were lower after treatment th an before. After cetirizine, the threshold concentration was significa ntly higher (217 mg/mL) than after ebastine (0.82 mg/mL) (P < .001), a nd total inhibition of the wheal reaction was observed in 21 of 24 pat ients at the lowest histamine concentration and in 17 of 24 at the hig hest. Ebastine never totally inhibited reaction, even to 5 mg/mL of hi stamine. Over the entire concentration-response curve, the coefficient of variation for the wheal reaction was 6.3% for cetirizine and 72.6% for ebastine, and, for flares, 11.0% and 83.7%, respectively. Hence, variability was much lower after cetirizine. Conclusion: Our study sho ws clearly that the efficacy of a single therapeutic dosage of cetiriz ine is consistently good for suppression of cutaneous reactivity to hi stamine in healthy volunteers. The need for ebastine to metabolize int o the active carebastine might explain its lesser consistency.