Antihistamines in urticaria and angioedema.

H1-antihistamines are the cornerstone of symptomatic treatment in acute and chronic urticaria, in which they not only relieve itching, but also reduce the number, size, and duration of urticarial lesions. Relief of whealing, flaring, and erythema may be incomplete as the vascular effects of histamine are mediated to its action at H2-receptors as well as at H1-receptors, and other vasoactive substances may also be involved. In randomized, prospective, placebo-controlled, double-blind studies, the new low-sedating H1-antihistamines have been found to be effective and safe in urticaria. Sedating antihistamines, although effective, place patients at risk for adverse effects, including decreased psychomotor performance. The response to H1-antihistamines in some types of urticaria, for example, in urticarial vasculitis, is unsatisfactory. An H2-antihistamine administered concurrently with an H1-antihistamine may modestly enhance relief of itching and wheal formation in some patients with urticaria refractory to treatment with an H1-antihistamine alone. The available evidence does not justify the routine addition of H2-antihistamine treatment to H1-antihistamine treatment.