A Study to Evaluate the Efficacy and Safety of Meptin® Swinghaler® and Ventolin® MDI in Stable Asthma Patients

Inclusion Criteria: 1. Male or females outpatients aged ≥ 16 years old with stable mild to moderate persistent asthma; Stability was assessed the patient remained in the same severity class (mild, moderate) and had no acute exacerbations by investigator judgment during the past 14 days; 2. Pulmonary function test: * Improvement ≥12% reversibility in FEV1 or FVC following administration of an inhaled β2-agonist before the study or ; * Positive result of Broncho-provocation test (PC20 ≤ 32 mg/ml) before the study. 3. Baseline forced expiratory volume in one second 60% ≤(FEV1)≤ 90% of predicted value on entry of the study; Exclusion Criteria: 1. Hypersensitivity to β2-agonist or lactose; 2. Hospitalization due to asthma during the previous 3months; 3. Respiratory tract infection requiring treatment with antibiotics in the previous 4 weeks; 4. Oral or systemic corticosteroids in the previous 4weeks; 5. Inadequately controlled hyperthyroidism; 6. Severe hepatic or renal or cardiovascular disease as judged by the investigator; 7. Patients receive an investigational drug within 30 days prior to admission to the study; 8. Patients with significant alcohol, drug or medication abuse as judged by the investigator; 9. Females who are pregnant or breast-feeding; (exception: Females of child-bearing age might be included, if in the opinion of the investigator, they are using adequate contraceptive precautions).