Tolerance to the protective effects of salmeterol on methacholine-induced bronchoconstriction: influence of inhaled corticosteroids

Long-acting beta2-adrenoceptor agonists such as salmeterol reduce airway responsiveness for at least 12 h, but this effect seems to decrease with regular use. We evaluated the time-course of the protective effects of salmeterol on methacholine-induced bronchoconstriction, its modulation by inhaled corticosteroids (ICS) and its influence on asthma control. Thirty two subjects (13 males and 19 females) with mild to moderate stable asthma were divided into two groups according to their medication needs: bronchodilators (BD) alone (n=16) or with ICS (n=16). After a 2 week run-in period, a double-blind crossover study was conducted. Subjects from both groups received salmeterol 50 microg b.i.d. or a placebo for 4 weeks each in random order, separated by a 2 week washout period. The provocative concentration of methacholine causing a 20% fall in forced expiratory volume in one second (PC20) was measured before and after each treatment period, 1 h prior to inhalation of salmeterol or placebo and 1 and 12 h after. Baseline forced expiratory volume in one second (FEV1) increased significantly after salmeterol, both after the first dose and at 4 weeks (BD group: 19 and 17%; ICS: 22 and 13%). On the first day of administration, salmeterol provided significant protection in both groups up to 12 h with a PC20 before and 1 and 12 h postdose of 2.2, 21.7 and 12.4, mg x mL(-1), respectively, in the BD group and 2.1, 11.6 and 55 mg x mL(-1), respectively, in the ICS group. After 4 weeks, this effect was significantly attenuated in both groups with a PC20 before, 1 and 12 h postdose of 3.3, 10.9 and 7.1 mg x mL(-1), respectively, in the BD group and 2.1, 5.0 and 2.3 mg x mL(-1), respectively, in the ICS group. This loss of protective effect was of similar magnitude in both groups. Respiratory symptoms, rescue beta2-agonist use and baseline FEV1 did not change significantly throughout the study in both groups. In conclusion, the bronchoprotective effect of salmeterol decreased with regular use both 1 and 12 h postdose; inhaled corticosteroids did not prevent this reduction. However, the development of tolerance was not associated with loss of asthma control.

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