H1-Receptor Antagonists in the Management of Allergic Rhinitis
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- Kontou-Fili, K. Clin. Immunother. (1994) 2: 352. doi:10.1007/BF03259495
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Allergic rhinitis, the most common clinical expression of atopy, is caused by: (a) the action of various mediators and other cell-derived substances released during the acute phase of the allergic reaction; and (b) the inflammatory response that follows hours later. Histamine, a mediator of major importance in eliciting the signs and symptoms of allergic rhinitis, is known to act via a number of distinct receptors (H1, H2, H3 and possibly H4). It appears that H1-receptors are functionally most important in the nose, and hence H1-receptor antagonists have been the mainstay of rhinitis treatment for over 50 years.
Classic first-generation antihistamines freely cross the blood-brain barrier and also exhibit significant anticholinergic activity, causing sedation and other adverse effects that restrict their use. Second-generation nonsedating H1-antagonists have fewer adverse effects, are longer acting, permitting a more convenient dosage schedule, and also exhibit additional antiallergic properties. Such features are probably more important in the chronic forms of rhinitis, where second-generation agents should preferentially be employed.
No single H1-antagonist, old or new, controls nasal blockage adequately. As a consequence, the demand for combining antihistamines with sympathomimetic vasoconstrictors has been more or less constant, despite the introduction of the improved second-generation H1-antagonists. Several of the nonsedating antihistamines are presently available in fixed combinations with pseudoephedrine and might be used in cases of persistent nasal blockage. Combination of H1- and H2-antagonists, even when applied locally, does not appear to alleviate the symptoms of rhinitis more than monotherapy with H1-antagonists.
Caution must be observed when considering H1-antagonist therapy for special groups of patients. These situations include extremes of age, pregnancy, lactation, individuals with impaired renal or hepatic function, and those who are receiving drugs known to interact with particular antihistamines.
Asthma coexisting with rhinitis does not constitute a contraindication for the use of H1-antagonists. Second-generation antihistamines are particularly appropriate in this situation, not only because they are free of anticholinergic adverse effects such as drying of mucous membranes, but also because some of them exhibit additional antiallergic properties and/or mild anti-inflammatory activity.