- PC20 < 4 mg/ml per methacholine inhalation test using standardized methods, for patients with pre-bronchodilator FEV1 ≥60% predicted (or FEV1 > lower limit defined by individual hospital protocol). PC20 is the provocative concentration of Provocholine® (a brand of methacholine chloride) resulting in a drop of FEV1 of 20% or more from Baseline