 This study will consist of a prospective, open-label, randomized, controlled trial conducted in 24 patients with cystic fibrosis. Twenty subjects will be stratified in a 1:2 ratio based on baseline FEV1 into mild 70 or moderate 40-70 pulmonary disease in order to control for disease severity within each dose level. The subjects will be randomized in blocks of four to receive no drug, 40mg, 100mg, or 200mg daily for 28 days. 