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

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Abstract
Background: This randomized, double‐blind, crossover study compared the effects of the R‐enantiomer of cetirizine, levocetirizine, with those of loratadine on the wheal, flare, and itch response to histamine in human skin. Methods: Levocetirizine (5 mg), loratadine (10 mg), or placebo was taken orall_y 4 h before the intradermal injection of histamine (20 µl, 100 µM) or the control vehicle into the forearm skin of healthy volunteers. Flare areas were assessed by scanning laser Doppler imaging before and at 30‐s intervals for a period of 9 min. Wheal areas were measured by planimetry at 10 min. 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 cm2, the wheal area 248±27 mm2, and the cumulative itch score 28.8±4.6% (mean±SEM). Levocetirizine reduced the flare, wheal, and itch by 60%, 68%, and 91%, respectively (all_ Pt‐test for paired data). The effects of loratadine were variable and not statisticall_y 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.