Glycemic Stability of Insulin Aspart Versus Insulin Lispro in Insulin Pump Therapy

The purpose of this study is to determine:

1. whether there is a difference between insulin aspart and insulin lispro in continuous insulin pump therapy
2. whether duration of the insulin infusion set placement effect blood sugar control if the infusion set is in place for longer then 72-96 hours

Insulin instability in pump infusion systems can result in unexplained hyperglycemia in patients on continuous subcutaneous insulin infusion (CSII) therapy. We have noted that some pump patients develop glycemic instability with use of insulin lispro, and that this resolves with change to insulin aspart. Several patients using lispro have reported noting a whitish precipitate in the infusion set, and in two cases we have examined the catheters and confirmed biochemically that this precipitate was insulin. Furthermore, in vitro studies indicate that insulin aspart is more resistant to isoelectric precipitation than insulin lispro. Although it has been rare for patients to notice a visible precipitate in the pump catheter, there is a subset of patients using lispro who have noted that their blood glucose levels will tend to rise 2 or more days after the insertion of a new pump infusion system. These findings mirror bench studies showing that the relative stability differences between aspart and lispro in pump infusion systems becomes more apparent over time.

The endpoints examined in previous randomized clinical trials comparing aspart and lispro were not directed specifically at assessing the effect of insulin type on glycemic stability. In these previous studies, pump infusion systems were changed every 48 hours whereas most pump patients routinely replace their infusion catheters only every 72-96 hours; this discrepancy may account for the failure of these trials to demonstrate the difference in the stability of insulin aspart and lispro that has been noted in clinical practice.

This investigator-initiated clinical trial is intended to assess the safety and efficacy of CSII with insulin aspart compared to insulin lispro with use of pump infusion catheters for up to 96 hours.

Eligibility Criteria:
Inclusion Criteria:

* Type 1 diabetes treated with CSII at least 3 months.
* Males and females, \> 18 years but \< 75 years old.
* Hemoglobin A1c ≤ 8.0 % at measurement taken at week 0 (screening visit).
* Duration of diabetes ≥ 12 months.
* Willingness to perform self-blood glucose monitoring several times/day.

Exclusion Criteria:

* Previous insulin precipitation in pump infusion catheters.
* Daily insulin requirements \> 25% of pump reservoir capacity. (This would preclude the subject from using the pump infusion system for more than 3 days).
* Use of an insulin pump that does not have a downloadable record of basal and bolus doses.
* Known or suspected allergy to trial products.
* Pregnancy, breast-feeding, intention to become pregnant or inadequate contraception measures.
* Known or suspected alcohol or drug abuse.
* Impaired renal function with creatinine ≥ 1.7 mg/dl.
* Pronounced catheter site scarring.
* Chronic use of drugs that may influence glycemic control (e.g. steroids).
* Any other significant concomitant disease that would interfere with participation in and completion of the trial.