Effects of treatment with formoterol on bronchoprotection against methacholine

In addition to their bronchodilatory effects, beta(2)-agonists protect against bronchoconstriction, such as that caused by methacholine challenge. However, tachyphylaxis to this beneficial effect develops after chronic use of beta(2)-agonists. We studied whether the frequency or dose of treatment with a long-acting beta(2)-agonist (formoterol) affects the degree of bronchoprotection afforded against methacholine challenge and to compare this with the effects of a short-acting beta(2)-agonist (terbutaline).

In a randomized, parallel group, double-blind study at two centers, patients with stable asthma of mild to moderate severity who were treated with inhaled corticosteroids were treated with formoterol 6 micrograms twice daily, 24 micrograms twice daily, 12 micrograms once daily; terbutaline 500 micrograms four times daily; or placebo. Treatments were given by dry powder inhaler for a period of 2 weeks. Of the 72 patients who were enrolled, 67 completed the study. Methacholine challenge was performed to calculate the provocative dose that caused a 20% fall in forced expiratory volume in 1 second at baseline (unprotected) after an initial 1-week run-in without beta(2)-agonists, 1 hour after the first dose of study treatment, and again 1 hour after 7 and 14 days of study treatment.

Each of the four active treatments exhibited significant tachyphylaxis (P < 0.05) to protection against methacholine challenge when comparing first/last dose (as geometric mean protection ratio versus baseline): formoterol 24 micrograms twice daily (9.6-fold/1.6-fold), 12 micrograms once daily (7.1-fold/2.2-fold), 6 micrograms twice daily (6.2-fold/2.3-fold), and terbutaline 500 micrograms four times daily (2.9-fold/2.0-fold). There were no significant differences among treatments after 2 weeks in bronchoprotection against methacholine challenge. For all formoterol regimens, the bronchodilator response 1 hour after inhalation was maintained over the 2-week treatment period. Diurnal control of morning and evening peak flow was significantly better with formoterol 24 micrograms twice daily than with terbutaline.

Tachyphylaxis to bronchoprotection against methacholine challenge develops after 2 weeks of therapy with formoterol, a long-acting beta(2)-agonist, at all three dosage regimens that were tested. In contrast, the bronchodilator effects of formoterol were maintained during the 2 weeks of treatment.