Background: H1 antihistamines (anti-H1) are the treatment of choice in chronic urticaria. We report five cases of urticaria, induced or aggravated by H1 antihistamines.
Methods: The immunoallergological investigations included prick-tests and intradermal tests with the antihistamine responsible for acute urticaria.
Results: The skin tests confirmed the non-IgE dependent nature of the urticarial eruptions and anti-leukotrienes (montelukast, Singulair) were effective in controlling chronic urticaria in 3/4 patients.
Discussion: Two hypotheses are discussed to explain the paradoxical aggravating effect of H1 antihistamines on the urticaria: 1) the patients are sensitive to the toxic, pro-inflammatory effect of the drug, which is the source of nonspecific activation of mast cells; 2) the fact that the urticaria is sensitive to anti-leukotrienes suggests that histamine is not the principal mediator of urticaria in these patients.