This is a Phase 2, multi-center, double blind, placebo controlled study to evaluate the safety and tolerability of PBI-4050, and its effects on the pancreatic, pulmonary functions and on various biomarkers in Cystic Fibrosis patients with abnormal glucose tolerance. Patients with abnormal glucose tolerance have elevated glucose level either at 1 hour or 2 hour during an Oral Glucose Tolerance Test (OGTT). The Main study will include 24 weeks of treatment with PBI-4050 or matching placebo. At the end of the treatment period, patients will have the option of participating in a 24-week Extension study.