Effects of formoterol or salmeterol on impulse oscillometry in persistent asthma

Background

Effects of small-particle long-acting β-agonists on the small airways have been poorly documented.
Objective

We used impulse oscillometry (IOS) to compare single and repeated dosing effects of small- and large-particle long-acting β-agonists.
Methods

After a 1- to 2-week run-in period, patients received either 12 μg of small-particle hydrofluoroalkane 134a–formoterol solution or 50 μg of large-particle salmeterol dry powder twice daily plus inhaled corticosteroid for 1 to 2 weeks with a 1- to 2-week washout period in between. Measurements were made over 60 minutes after the first and last doses.
Results

Sixteen patients completed the study as follows: mean age, 43 years; FEV1, 80%; forced midexpiratory flow between 25% and 75% of forced vital capacity (FEF25-75), 48%; total airway resistance at 5 Hz, 177%; peripheral airway resistance as the difference between 5 and 20 Hz, 0.18 kPa·L−1·s; Asthma Control Questionnaire score, 0.76; and inhaled corticosteroid dosage, 550 μg/d. There were significantly greater improvements with formoterol versus salmeterol in all IOS outcomes and FEF25-75, but not FEV1, at 5 minutes after the first dose, which were not sustained over 60 minutes. After the last dose, all IOS outcomes, but not FEV1 or FEF25-75, were significantly better with formoterol over the entire 60 minutes: mean difference at 60 minutes between formoterol and salmeterol in total airway resistance at 5 Hz, 7.50% (95% CI, 1.56% to 13.43%, P = .02); central airway resistance at 20 Hz, 5.37% (95% CI, 0.13% to 10.62%, P = .045); peripheral airway resistance as the difference between 5 and 20 Hz, 12.76% (95% CI, 1.28% to 24.24%, P = .03); reactance area under the curve, 19.46% (95% CI, 7.56% to 31.36%, P = .003); reactance at 5 Hz, 11.19% (95% CI, 4.62% to 17.76%, P = .002); and resonant frequency, 9.34% (95% CI, 3.21% to 15.47%, P = .005). Peak expiratory flow significantly improved to a similar degree with both drugs.
Conclusion

Significant improvements in IOS outcomes but not spirometry results occurred after chronic dosing with formoterol compared with salmeterol. This might reflect better deposition to the entire lung, including the small airways.