Combined Antagonism of Leukotrienes and Histamine Produces Predominant Inhibition of Allergen-Induced Early and Late Phase Airway Obstruction in Asthmatics

We defined the contribution of histamine and leukotrienes to allergen-induced airway obstruction in asthmatics; 12 subjects with allergic asthma underwent identical allergen bronchoprovocations on four occasions. At a control session, all subjects displayed early (EAR) and late asthmatic (LAR) reactions. The mean (+/- SE) drop in FEV1 during EAR (0-2 h) and LAR (2-12 h) was 29 +/- 2% and 28 +/- 4%, respectively. Thereafter, the influence of 1 wk randomized pretreatment with the leukotriene receptor antagonist zafirlukast (Accolate) (80 mg twice daily), the antihistamine loratadine (10 mg twice daily), and the combination of both antagonists was assessed. Expressed as AUC FEV1 in percent of the control reaction, zafirlukast reduced the response during EAR and LAR by 62 +/- 11% and 55 +/- 12%, respectively (p < 0.05 versus control). Loratadine inhibited EAR and LAR by 25 +/- 14% and 40 +/- 16%, respectively (p < 0.05 versus control). Zafirlukast was significantly more effective than loratadine during EAR but not during LAR. The combination of zafirlukast and loratadine reduced the AUC FEV1 during EAR and LAR further, by 75 +/- 8% and 74 +/- 14%, respectively (p < 0.05 versus control). The combination was significantly (p < 0.05) more effective than either drug alone during the LAR. The findings indicate that leukotrienes and histamine together mediate the major part of both the EAR and the LAR following exposure of asthmatics to allergen. Combination of leukotriene antagonism and antihistamines may represent a new strategy for treatment of airway obstruction in asthma.