Cystic Fibrosis (CF) is a chronic disease characterized by recurrent pulmonary infections and exocrine pancreatic insufficiency. The vast majority of patients with CF will develop pancreatic endocrine insufficiency over time manifested as altered glucose metabolism. The presence of overt diabetes in patients with CF is associated with adverse clinical outcomes.

The underlying pathophysiology of cystic fibrosis related diabetes (CFRD) is still a matter of investigation. In addition to localized tissue damage developing similar to that of the exocrine pancreas, additional mechanisms may be involved. The investigators have recently shown that insulin secretion in patients with CF is significantly altered prior to the development of diabetes. This phenomenon is associated with reduced secretion of gut derived incretins (specifically GIP). The blunting of incretin induced insulin secretion (whether due to a deranged interaction of gastrointestinal contents with enterocytes resulting in reduced secretion or due to rapid clearance of such peptides) may be a major underlying driver of altered glucose metabolism in such patients.

Inclusion Criteria:

• Age > 18 years
• No diabetes based on screening OGTT
• No C/I for use of the medications
• Normal kidney function
• Willing and able to participate

Exclusion Criteria:

• Use of anti-hyperglycemic medications
• Acute illness or infection at enrollment