Study funding was for 1 year to a fellow who graduated in early stages of enrollment. While 6 patients were enrolled, many patients didn't finish the study and therefore little data was collected and no results will be entered.

The purpose of the study is to evaluate the effect of sitagliptin on overall blood glucose concentrations in Type I Diabetic subjects. The study also aims to evaluate post meal glucagon concentrations in Type I Diabetic subjects (a possible mechanism of reduced blood glucose concentrations) and indices of oxidation stress in the plasma of these subjects.

The hypothesis is that Sitagliptin will improve overall blood glucose, fasting blood glucose, and glycemic excursions in patients with Type I Diabetes. In addition, sitagliptin will likely suppress indices of oxidative stress in patients. The study will investigate proposed mechanisms of improved glucose concentrations, including enhanced effect of endogenous GLP-1 and suppression of glucagon.

Inclusion Criteria:

1. Male or female adult, aged 18 to 70 years
2. Type 1 Diabetes Mellitus for 6 months or more, as established by medical history
3. Current treatment with multiple injections of insulin (at least 4) or CSII (continuous subcutaneous insulin infusion or insulin pump) therapy for at least 3 months prior to screening visit; and using the same insulin during the last 1 month
4. HbA1c ≤ 8.5%
5. Subjects should routinely practice at least 2-4 blood glucose measurements per day
6. BMI ≤ 35 kg/m2
7. Subject must be able and willing to perform self-blood glucose monitoring and accept wearing a continuous glucose monitor for 3 days at the start and 3 days at the end of the study
8. Subjects must be willing to complete study visits per study protocol
9. Able to speak, read, and write English

Exclusion Criteria:

1. Type 1 Diabetes Mellitus for less than 6 months
2. Coronary Event or procedure (myocardial infarction, unstable angina, coronary artery bypass surgery, or coronary angioplasty) in the previous 4 weeks
3. Any other life-threatening, non-cardiac disease
4. Pregnant or intends to become pregnant during the course of the study
5. Severe unexplained hypoglycemia that required emergency treatment over the past 3 months
6. History of hemoglobinopathies
7. Post-renal transplantation, currently undergoing dialysis, creatinine of >1.5mg/dl or a calculated creatinine clearance of <50 mL/min.
8. Have extensive skin changes/diseases that inhibit wearing the sensor on normal skin
9. Subjects who have an allergy to medication being used
10. Current participation in another study protocol
11. History of autonomic neuropathy or gastroparesis