Comparative in vivo bioactivity of modern H1-antihistamines on AMP challenge in atopic asthma.

Abstract

Modern H(1)-antihistamines differ in their in vitro binding affinity, but their comparative in vivo bioactivity in asthmatic airways is unknown. We compared clinically recommended doses of 3 H(1)-antihistamines on airway hyperresponsiveness to AMP challenge (the primary outcome variable). Sixteen atopic patients with mild-to-moderate asthma of whom 10 were receiving inhaled corticosteroid therapy (all had positive results to house dust mite on skin prick testing) were randomized in a double-blind, placebo-controlled, cross-over fashion to receive single doses of 5 mg of desloratadine, 180 mg of fexofenadine hydrochloride (FEX), 5 mg of levocetirizine dihydrochloride (LEV), or placebo, with AMP challenge performed 12 hours after dosing. All H(1)-antihistamines demonstrated significantly greater (P <.05) geometric mean +/- SEM AMP PC(20) values compared with that of placebo (86 +/- 29 mg/mL): desloratadine, 189 +/- 54 mg/mL; FEX, 176 +/- 57 mg/mL; and LEV, 163 +/- 48 mg/mL. Prechallenge forced expiratory flow at 25% to 75% of maximal lung volume (percent predicted) but not FEV(1) was significantly higher (P <.05) for all H(1)-antihistamines compared with that of placebo (53% +/- 4%): desloratadine, 62% +/- 4%; FEX, 62% +/- 4%; and LEV, 59% +/- 3%. There were no significant differences in either AMP PC(20) or lung function values among the H(1)-antihistamines. Single doses of H(1)-antihistamines improved airway hyperresponsiveness and small-airways caliber to a similar degree. Data for in vitro binding affinity do not therefore translate into commensurate differences in in vivo bioactivity at clinically recommended doses.