The purpose of this study is to determine the effects of sitagliptin on glucose variability both after meals and overnight in adult patients with type 1 diabetes.

Improved post prandial glucose control with multiple daily injections of insulin in the DCCT study demonstrated significant reductions in microvascular complication. Similar to type 2 diabetes, patients with type 1 diabetes have a paradoxical increase in glucagon after meals which contribute to worsening post prandial glucose control. This proposed study is designed to determine if altering the glucagon axis by giving sitagliptin can improve glucose control in patients with type 1 diabetes.

Inclusion Criteria:

• Male or female adult, aged 18 to 70 years
• Type 1 diabetes mellitus as established by medical history
• Current treatment with MDI or CSII therapy for at least 3 months prior to screening visit; and using the same insulin during the last 1 month
• HbA1c ≥ 8.5%
• Subjects should routinely practice at least 2-4 blood glucose measurements per day
• BMI ≤ 35 kg/m2
• Subject must be able and willing to perform self-blood glucose monitoring and accept wearing a continuous glucose monitor for the total duration of the study
• Willing to complete a routine medical visits every 3 months
• Willing to complete a total of 7 phone visits
• Able to speak, read, and write English

Exclusion Criteria:

• On oral, inhaled or pre-mixed insulin
• On Symlin
• BMI > 35 kg/m2
• Pregnant or intends to become pregnant during the course of the study
• Severe unexplained hypoglycemia that required emergency treatment over the past 3 months
• History of hemoglobinopathies
• Diagnosis of anemia
• HbA1C greater than 12%
• Post-renal transplantation, currently undergoing dialysis, creatinine of >1.5mg/dl or a calculated creatinine clearance of <50 mL/min.
• Have extensive skin changes/diseases that inhibit wearing the sensor on normal skin
• Subjects who have a medical known allergy to adhesives
• Subjects who have an allergy to medication being used
• Currently participation in another investigational study protocol. Must have completed a previous study at least 30 days prior to being enrolled in this one
• Have any condition that, in the opinion of the Investigator, would interfere with their participation in the trial.