Antihistamines and allergic asthma

Subjects with asthma demonstrate hyperresponsive airways to histamine and require only small quantities of this mediator to demonstrate changes in their pulmonary functions. The discovery of drugs that could compete with and antagonize the target-tissue effects of histamine has provided a method of testing whether histamine contributes as a mediator of asthma. Now, there are potent and selective anti-H, drugs which are relatively non sedating. Some of them inhibit the bronchoconstrictions induced either by allergen or exercise (e.g. terfenadine, astemizole, azelastine); some others, moreover, inhibit mast cell degranulation (e.g. azelastine). Finally, some others (e.g. cetirizine, ketotifen) display some inhibitory actions on eosinophil functions, an important cell in allergic cellular recruitment and inflammation. Some studies with H1 antihistamines in asthma have demonstrated some therapeutic benefits. However, additional carefully controlled studies are required to confirm their efficacy in asthma.