The therapeutic ratio of R-albuterol is comparable with that of RS-albuterol in asthmatic patients.
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% FEV(1) reversibility) were given R-albuterol (6.25-1600 microg), S-albuterol (6.25-1600 microg), RS-albuterol (12.5-3200 microg), or placebo in a crossover, double-blind, placebo-controlled fashion. Cumulative doses were given with a Mefar dosimeter, and FEV(1), heart rate, and plasma K(+) levels were measured 20 minutes after each dose.


RESULTS
Both R- and RS-albuterol produced dose-related improvement in FEV(1) and, 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 FEV(1) was 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).


CONCLUSIONS
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 (FEV(1)) and systemic effects (heart rate and K(+)) are similar, suggesting a comparable therapeutic ratio for R-albuterol and RS-albuterol in asthmatic subjects.
Lötvall
J
J
Department of Respiratory Medicine and Allergology, Göteborg University, Göteborg, Sweden.
Palmqvist
M
M
Arvidsson
P
P
Maloney
A
A
Ventresca
G P
GP
Ward
J
J
D000328:Adult; D000368:Aged; D000420:Albuterol / Q000009:adverse effects / Q000737:chemistry* / Q000493:pharmacokinetics / Q000627:therapeutic use*; D001249:Asthma / Q000188:drug therapy* / Q000378:metabolism; D001993:Bronchodilator Agents / Q000009:adverse effects / Q000737:chemistry* / Q000493:pharmacokinetics / Q000627:therapeutic use*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000097:blood; D013237:Stereoisomerism
D001993:Bronchodilator Agents; D000420:Albuterol; D011188:Potassium