To Confirm Equivalent Bronchodilator Efficacy of the Test Product Compared to the Reference Product

Main inclusion criteria: * Written informed consent * Asthma diagnosis for at least 6 months * Prebronchodilator FEV1 45-90% of the predicted value * Demonstration of reversible airway obstruction * Stable asthma on the same regular treatment for at least 4 weeks before the study * Non-smoker for at least 6 months before the study Main exclusion criteria * Respiratory infection within 4 weeks before the study * Smoking history of more than 10 pack-years * Other severe chronic respiratory disease than asthma * Concurrent illness that would interfere with the interpretation of the study results or constitute a health risk for the patient if he/she takes part in the study * Corrected QT interval \> 450 ms in males or \> 470 ms in females * Abnormal serum potassium value or other clinically significant laboratory finding * Systolic blood pressure over 180 mmHg and/or diastolic blood pressure over 100 mmHg * Treatment with a long-acting β2-agonist, a xanthine-derivative, a β-blocker or with a corticosteroid (other than inhaled) within 4 weeks before the study * Use of drugs that prolong QT-interval * Women who are pregnant, breast-feeding or without reliable contraception * Participation in another clinical drug study