Background: It has been suggested that R-albuterol produces bronchodilation that is comparable with that of racemic albuterol (RS-albuterol) on a 4:1 dose-for-dose basis but systemic side effects on a 2:1 basis, implying better therapeutic ratio for R-albuterol. Objective: We sought to carefully compare the bronchodilating and systemic effects of R- and RS-albuterol by using a crossover study design. Methods: Twenty asthmatic patients (15.1%-28.7% FEV1reversibility) were given R-albuterol (6.25-1600 μg), S-albuterol (6.25-1600 μg), RS-albuterol (12.5-3200 μg), or placebo in a crossover, double-blind, placebo-controlled fashion. Cumulative doses were given with a Mefar dosimeter, and FEV1heart rate, and plasma K+levels were measured 20 minutes after each dose. Results: Both R- and RS-albuterol produced dose-related improvement in FEV1and, at higher doses, increased heart rate and decreased plasma K+levels. Neither placebo nor S-albuterol had any significant effect. Individual estimates of the potency ratio for R-albuterol/RS-albuterol were calculated and summarized across all subjects. The geometric mean potency ratio for effects on FEV1was 1.9 (95% CI, 1.3-2.8), on HR of 1.9 (95% CI, 1.3-2.9), and on K+level of 1.7 (95% CI, 1.3-2.1). Conclusion: All pharmacologic effects of RS-albuterol reside with the R-enantiomer, and S-albuterol is clinically inactive. The R-albuterol/RS-albuterol potency ratios for local (FEV1) and systemic effects (heart rate and K+) are similar, suggesting a comparable therapeutic ratio for R-albuterol and RS-albuterol in asthmatic subjects. © by Mosby, Inc.
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