Effect of Magnitude of Airway Responsiveness and Therapy With Inhaled Corticosteroid on Histamine Tachyphylaxis in Asthma

Histamine challenge testing is used to measure airway responsiveness in asthma. Histamine tachyphylaxis has been demonstrated after repeated challenges in mild asthmatics not using inhaled corticosteroid. Other studies, using subjects with variable severity of asthma, have not demonstrated histamine tachyphylaxis. Forty patients with stable asthma were studied and stratified according to severity of airway hyperresponsiveness and use of inhaled corticosteroid, to examine the effects of these factors on histamine tachyphylaxis. Airway responsiveness was measured as the histamine provocative concentration causing a 20 percent fall in FEV1 (PC20). Twenty subjects had mildly increased airway hyperresponsiveness (PC20 > 1 mg/ml), of whom 10 were using inhaled corticosteroid. Twenty subjects had moderate to severely increased airway hyperresponsiveness (PC20 < 1 mg/ml), of whom 10 were using inhaled corticosteroid. On each of two study days, 1 week apart, two histamine challenges were performed 1 h apart. Histamine tachyphylaxis was found for the entire group on both study days. The geometric mean PC20 increased from 1.0 mg/ml (percent SEM 1.2) to 1.3 mg/ml (percent SEM 1.2) 1 h later on day 1 (p < 0.0005), and 1.1 mg/ml (percent SEM 1.2) to 1.3 mg/ml (percent SEM 1.2) 1 h later on day 2 p < 0.05). Subgroup analysis demonstrated that tachyphylaxis only occurred consistently in subjects with mildly increased airway hyperresponsiveness not receiving inhaled corticosteroid. In this group, the PC20 increased from 2.2 mg/ml (percent SEM 1.2) to 3.2 mg/ml (percent SEM 1.2) on day 1 (p < 0.001), and from 2.5 mg/ml (percent SEM 1.3) to 3.4 mg/ml (percent SEM 1.2) on day 2 (p < 0.05). This study confirms that histamine tachyphylaxis occurs in asthmatics, but is consistently present only in mild, noncorticosteroid-dependent asthmatics.