Background: Formoterol and salmeterol differ in their relative intrinsic activity at airway beta(2)-adrenoceptors, with formoterol being a full agonist. The homozygous glycine-16 polymorphism of the beta(2)-adrenoceptor occurs in approximately 40% of patients and is known to predispose to agonist-induced downregulation and desensitization.
Objectives: To evaluate possible differences in intrinsic beta(2)-adrenoceptor agonist activity between salmeterol and formoterol in terms of their functional antagonism against methacholine-induced bronchoconstriction (the primary end point) in genetically susceptible patients who exhibited the homozygous glycine-16 polymorphism.
Methods: Eighteen patients with mild-to-moderate persistent asthma receiving inhaled corticosteroid who expressed the homozygous glycine-16 genotype were randomized to completion (mean [SEM] age, 35.8 [3.2] years; mean FEV(1), 76.9 [2. 5]% predicted). Patients received three different treatments for 1 week in randomized, double-blind, crossover fashion, with a 1-week washout period between treatments: formoterol, 12 microg bid; salmeterol, 50 microg bid; and placebo. For each of the randomized treatment periods, there were three separate methacholine challenges: baseline after washout, 12 h after the first dose, and 12 h after the last dose.
Results: Both salmeterol and formoterol exhibited significantly (p < 0.05) greater bronchoprotection than placebo for their effects after single or repeated dosing, although there was no significant difference between the two drugs. The geometric mean fold protection vs placebo (95% confidence interval [CI]) for the first dose was 1.6-fold (95% CI, 1.1 to 2.2) for salmeterol and 1.9-fold (95% CI, 1.1 to 3.2) for formoterol, and for last dose was 1.6-fold (95% CI, 1.2 to 2.3) for salmeterol and 1. 9-fold (95% CI, 1.2 to 2.8) for formoterol. Salmeterol and formoterol produced significant (p < 0.05) increases in FEV(1) and forced expiratory flow after 25 to 75% of vital capacity has been expelled, after the first but not the last dose compared to placebo, while there were significant (p < 0.05) improvements in domiciliary peak flows during treatment with both drugs.
Conclusion: Our results showed no difference between formoterol and salmeterol in the degree of functional antagonism against methacholine-induced bronchoconstriction at the end of a 12-h dosing interval in patients who expressed the homozygous glycine-16 genotype. There was a significant residual degree of bronchoprotection after 1 week of treatment, which was not significantly different compared to the first-dose effect.