 - Other medication usage: Patients unable or unwilling to be withdrawn from hypertonic saline therapy for two weeks prior to Visit 1 baseline MCC visit. Patients using Pulmozyme will be permitted to participate in this trial. Patients on chronic, cycling antibiotics will be required to have completed at least 2 full cycles of the prescribed antibiotic prior to enrollment and should not cycle on or off this therapy during the treatment period of the study. 