2. Patients who have unstable lung disease as defined by the requirement for intravenous antibiotics during the four weeks prior to screening, a change in medical regimen within 14 days prior to administration of the first dose of study drug or during the 14 day treatment period, a FEV1 ≥ 15% below recent (within six months) clinical measurements, or significant new findings on chest radiograph (pneumothorax, lobar/segmental collapse) that are not considered a part of the usual, chronic progression of cystic fibrosis lung disease.