- Previously documented diagnosis of asthma of ≥ 1 year duration, based on episodic symptoms of airflow obstruction; post-bronchodilator reversibility of airflow obstruction ≥ 12% (at screening or documented within 1 year prior to randomization); or proof of a positive response to a methacholine challenge (documented within 1 year prior to randomization) as represented by a provoking concentration of methacholine to cause a 20% fall in forced expiratory volume in 1 second (FEV1); (PC20) < 8 mg/mL.