ADVANCES IN THE PHARMACOTHERAPY OF ALLERGIC RHINITIS - 2ND-GENERATIONH1-RECEPTOR ANTAGONISTS

Allergic rhinitis, whether seasonal or perennial, potentially affects up to 30% of the population. Pharmacotherapy for allergic rhinitis tha t is directed at symptomatic relief traditionally includes antihistami nes as one of the first lines of therapy. All antihistamines are H-1-r eceptor antagonists, or H-1 blockers; they are reversible, competitive inhibitors of the actions of histamine, a critical mediator in the pa thophysiology of the allergic response. Nearly all antihistamines (wit h the exception of the second-generation antihistamine cetirizine) are metabolized by the hepatic cytochrome P-450 system. Potentially fatal adverse effects of antihistamines may include heart arrhythmias from overdosage. Hepatic or cardiac dysfunction also predisposes to heart a rrhythmias in patients who take antihistamines. Concomitant administra tion of macrolide antibiotics or antifungal agents with antihistamines may also predispose patients to potentially fatal heart arrhythmias. First-generation H-1 blockers (e.g., the ethanolamines, ethylenediamin es, alkylamines, piperazines, and phenothiazines) offer rapid relief o f symptoms (usually within 15 or 30 minutes) but have the potential fo r significant sedation and for adverse reactions and drug interactions , as previously described. In contrast, however, the second-generation H-1-antagonists (e.g., clemastine, terfenadine, astemizole, acrivasti ne, loratadine, and cetirizine) offer equal or superior relief but hav e markedly decreased sedation potential. This article compares first- and second-generation H-1 blockers to provide clinicians with a better understanding of each agent's actions, potential side effects, and ef ficacy as antihistamine therapy.