The effects of one week's daily treatment with
dexchlorpheniramine (3 + 3 mg x 2) and
loratadine (10 mg x 2) on the cutaneous reactions to putative mediators of urticarial reactions were studied in healthy subjects and in patients with
chronic urticaria. Biopsy specimens were taken from skin with delayed reactions and studied immunohistochemically for the presence of eosinophilic cationic
protein (ECP). In healthy subjects both
antihistamines significantly decreased the weal and flare induced by
histamine and the
histamine releaser
compound 48/80. They also reduced the flare seen after injection of PAF (
platelet activating factor) and
kallikrein. In patients with
chronic urticaria the delayed reactions to PAF and
kallikrein were larger than in healthy subjects. The immediate flare seen after injection of
histamine, 48/80 and PAF, and the delayed reaction to 48/80, were significantly decreased by treatment with
loratadine. No correlation was found between the clinical response and test reactions. In the group of healthy subjects, eosinophils were increased in the skin of all subjects after
intradermal injection of 100 micrograms of PAF and in 50% after 1 microgram of PAF, but no eosinophils were seen after injection of 1 ng of PAF. In patients with
chronic urticaria the eosinophils were increased at all sites where 1 ng of PAF had been injected and also at a limited number of sites of injection of
histamine, 48/80,
kallikrein and saline. Treatment with the
antihistamines had no effect on the influx of eosinophils in the skin.