Efficacy and safety of antihistamines in allergic skin disorders

Background For patients with urticaria, H₁-antihistamines remain the gold standard medical treatment of choice. They act by blocking H₁ receptors on the vascular endothelial cell surface. Newer, non-sedating antihistamines such as loratadine also act to some extent by blocking the release of histamine from mast cells, basophils and human skin tissue. Efficacy All of the newer antihistamines (loratadine, terfenadine, astemizole and cetirizine) have been shown to have comparable efficacy to the classic sedating antihistamines and to be significantly superior to placebo in terms of symptom improvement. Loratadine has been shown to be at least as effective as the other non-sedating agents and cetirizine. Antihistamines also have a potential benefit in the management of patients with atopic dermatitis. In two studies, loratadine was found to be significantly superior to placebo in the reduction of pruritus. Safety In terms of safety, the newer antihistamines have important differences. Cetirizine, for example, causes dose-related sedation and functional impairment compared to placebo. In contrast, loratadine has no such sedative effects. Terfenadine and astemizole have also been shown to be free of sedative effects, but exceeding the recommended dose of either may increase the risk of a serious cardiac arrhythmia, torsades de pointes. Plasma levels of both terfenadine and astemizole may also be increased as a result of interaction with various drugs. In contrast, loratadine has not been shown to induce ECG changes, even at doses of 40 mg o.d. for 90 days.