Antihistamines in the treatment of clinical asthma.

Because the older antihistamines possessed relatively weak antihistaminic action, as well as sedative and anticholinergic effects, they could not be administered in doses high enough to confer relief to atopic patients with asthma. In contrast, the newer nonsedating, more potent H1-receptor antagonists appear to achieve effective histamine blockade in patients with asthma. Terfenadine and astemizole inhibit bronchoconstriction induced by inhaled allergens by 50% in the early asthmatic reaction. High-potency antihistamines also significantly reduce cough and wheeze as compared with placebo in grass pollen-sensitive asthma patients. Significant reductions in symptom severity and bronchodilator use were found with terfenadine, 120 mg twice daily, although these improvements may be confined to younger patients. Some of the newer antihistamines have demonstrated interesting effects on the late-phase allergic response. Azelastine partially inhibits bronchoconstriction in the allergen-induced late reaction of atopic persons with asthma, possibly by suppressing the release of additional inflammatory mediators. In the skin, cetirizine has been found to reduce eosinophil and neutrophil late-phase infiltration and prostaglandin D2 release. These interesting properties now warrant further investigation in clinical studies.