Tolerance to the bronchoprotective effect of β 2 -agonists: Comparison of the enantiomers of salbutamol with racemic salbutamol and placebo

Abstract

Background: Regular use of racemic salbutamol results in the partial loss of its bronchoprotective effect. The 2 enantiomers of salbutamol, the bronchodilator R-salbutamol and nonbronchodilator S-salbutamol, are now available. Objective: We sought to compare the effect of regular use of S-salbutamol, R-salbutamol, racemic salbutamol, and placebo on the bronchoprotective effect of a single dose of racemic salbutamol against methacholine-induced bronchoconstriction. Methods: Eleven of 13 well-controlled β 2 -agonist–free asthmatic subjects completed a double-blind, randomized study comparing racemic salbutamol 2.5 mg, S-salbutamol 1.25 mg, R-salbutamol 1.25 mg, and diluent placebo nebulized and inhaled 3 times daily for 6 days (≥6-day washout period). Ten to 12 hours after the last dose, the subjects performed measurement of FEV 1 , methacholine PC 20 , and a repeat methacholine PC 20 done 1 hour after the first methacholine test and 10 minutes after 2 puffs (200 μg) of racemic salbutamol administered from a metered-dose inhaler. The primary endpoint was the methacholine PC 20 dose shift (Δlog PC 20 ÷ log 2) from before to after administration of 200 μg of racemic salbutamol. Results: The methacholine dose shift was 3.2 doubling doses (9-fold increase in methacholine PC 20 after 200 μg of racemic salbutamol) during the placebo treatment and was unaltered (3.2) after administration of S-salbutamol. The dose shift was significantly lower after both the R-salbutamol and racemic salbutamol treatments (2.2 and 2.6 doubling doses, respectively); there was no significant difference between R-salbutamol and racemic salbutamol. There was no treatment effect on baseline FEV 1 , baseline methacholine PC 20 , or bronchodilation. Conclusion: Regular treatment with racemic salbutamol or R-salbutamol, but not S-salbutamol, results in a partial loss of bronchoprotection, without loss of bronchodilation, compared with placebo. (J Allergy Clin Immunol 1999;103:1049-53.)