Effect of Proton Pump Inhibitors on CF Pulmonary Exacerbations

Inclusion Criteria: 1. Cystic fibrosis 2. Age \> 18 years 3. Stable maintenance medical regimen during the previous 6 weeks. 4. Negative pregnancy test (women of childbearing potential) at both screening and baseline visits. 5. Women of childbearing potential must be using medically acceptable contraception. 6. At least two respiratory exacerbations per year requiring oral and/or intravenous antibiotics for each of the two years prior to study entry, but no more than 4 exacerbations requiring intravenous antibiotics during either of those years. Exclusion Criteria: 1. Previous anti-reflux or peptic ulcer surgery, 2. Use of proton pump inhibitor (PPI) within the past two weeks 3. Pulmonary exacerbation requiring antibiotics within the previous 2 weeks 4. Parenteral hyperalimentation 5. Cigarette smoking 6. Treatment with azoles, iron, anti-coagulants, digitalis 7. Use of any investigative drugs within the previous month. 8. Use of over the counter acid suppressor agents (not including acid neutralizers)