Inhaled β2 adrenoceptor agonists are frequently used to treat reversible lower airway obstruction, or to assist with mucociliary clearance. Albuterol remains the most commonly used β agonist and contains a racemic mixture of two enantiomers. The R enantiomer is the active moiety responsible for the bronchodilation, while the S enantiomer was initially thought to be inactive, although recent studies suggest otherwise. Levalbuterol contains the single R form enantiomer, and in clinical practice it is frequently prescribed not only because of its bronchodilator benefits, but to limit cardiovascular toxicity. Adverse cardiovascular effects remain the main dose-limiting factor for β2 agonists. The primary objective of the investigators study is to compare the change in oxygen consumption following albuterol to that of levalbuterol, in healthy adult volunteers. The investigators hypothesized there would be no clinically significant difference in V'O2 between the two drugs, if equal doses of the R-enantiomer were administered. Secondary objectives were to compare the changes in heart rate and other vital signs between the two drugs.
