Comparison of bronchodilatory properties of transdermal and inhaled long-acting β₂-agonists

Background: Regular use of long-acting bronchodilators is recommended for symptomatic COPD patients. A transdermal type of β₂-agonist, tulobuterol, was recently developed. This agent shows the pharmacokinetic property of a sustained serum concentration for 24 h. However, little has been reported about the bronchodilatory properties of this agent. Objectives: The aim of the present study was to compare the bronchodilatory action of transdermal β₂-agonist tulobuterol with that of inhaled long-acting β₂-agonist salmeterol. Methods: An open-label, randomized crossover study was performed. Eleven patients with stable COPD were enrolled in the study. Tulobuterol (2 mg/day) or salmeterol (50 μg, twice daily) was administered in a randomized, crossover manner. Forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and inspiratory capacity (IC) were measured before administration, every 2 h from 12 to 24 h, and at 36 h after the initial administration. Results: Transdermal β₂-agonist tulobuterol showed an improvement in FEV₁, FVC and IC after dosing compared with those at baseline. Salmeterol also improved all parameters of FEV₁, FVC and IC, and showed a greater improvement compared with the transdermal β₂-agonist tulobuterol (p<0.05). The values of the area under the curve (AUC) of FEV₁, FVC and IC during the administration of tulobuterol were 2.98±1.05, 1.81±0.98, 0.75±0.85 L h, respectively, and during the administration of salmeterol they were 6.39±1.12, 6.61±1.34, 4.28±0.91 L h, respectively. Conclusion: The transdermal β₂-agonist tulobuterol showed bronchodilatory action for at least 24 h by once daily administration. However, its bronchodilatory potency was about three times less than that of the inhaled β₂-agonist salmeterol.