Comparison of the effects of levocetirizine and loratadine on histamine-induced wheal, flare, and itch in human skin

Background: This randomized, double-blind, crossover study compared the eff ects of the R-enantiomer of cetirizine, levocetirizine, with those of lorat adine on the wheal, flare, and itch response to histamine in human skin. Methods: Levocetirizine (5 mg), loratadine (10 mg), or placebo was taken or ally 4 h before the intradermal injection of histamine (20 mul, 100 muM) or the control vehicle into the forearm skin of healthy volunteers. Flare are as were assessed by scanning laser Doppler imaging before and at 30-s inter vals for a period of 9 min. Wheal areas were measured by planimetry at 10 m in. Itch was scored every 30 s with a Visual analogue scale. Results: After placebo administration, the mean peak flare area was 23.01 /- 1.94 cm(2), the wheal area 248 +/- 27 mm(2), and the cumulative itch sco re 28.8 +/- 4.6% (mean +/- SEM). Levocetirizine reduced the flare, wheal, a nd itch by 60%, 68%, and 91%, respectively (all P<.001, Student's t-test fo r paired data). The effects of loratadine were variable and not statistical ly significant. Conclusions: Levocetirizine (5 mg) is a potent inhibitor of the effects of histamine in human skin with an efficacy that exceeded that of loratadine ( 10 mg) when single doses of the drugs were administered 4 h before the test .