Comparative efficacy of H1 antihistamines

Second-generation H1 receptor antagonists (cetirizine, terfenadine, astemizole, loratadine, azelastine, and acrivastine) offer several important advantages over the older first-generation antihistamines. They are substantially less sedating and have little or no anticholinergic activity. Many of them are effective for 12 to 24 hours, thereby increasing compliance. In addition to acting as competitive inhibitors of histamine, several seem to have other antiallergic mechanisms as well. They are all absorbed well when taken orally. Many studies demonstrate their effectiveness compared with placebo in the treatment of seasonal and perennial rhinitis and chronic urticaria, and several studies suggest that they have a role in the treatment of bronchial asthma. A number of multicenter, double-blind, placebo-controlled studies comparing the effectiveness of terfenadine, 60 mg bid, with chlorpheniramine, 8 mg bid, in seasonal allergic rhinitis demonstrate that both drugs are approximately equally potent in reducing the symptoms of sneezing, rhinorrhea, and nasal itching and are statistically significantly better than placebo. Ocular symptoms were reduced somewhat less but still significantly. No differences from placebo were recorded in their effect on nasal congestion. The effectiveness of cetirizine, 10 mg once daily, compared with astemizole, 10 mg once daily, was measured in double-blind, placebo-controlled studies of patients with seasonal allergic rhinitis. These studies also demonstrate statistically significant benefit from the study drugs compared with placebo in relieving all nasal symptoms except congestion. Both drugs also relieved ocular pruritus. Fewer studies have assessed azelastine, acrivastine, and loratadine, but all have been shown to provide significant relief of seasonal allergic rhinitis compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)