Comparison of in vitro stability for insulin aspart and insulin glulisine during simulated use in insulin pumps.

Background: This study was designed to evaluate the stability properties of the marketed insulin aspart (IAsp) and insulin glulisine (IGlu) products during simulated continuous subcutaneous insulin infusion (CSII) for up to 10 days.
Methods: Plastic reservoirs containing IGlu or IAsp were placed in MiniMed 508 infusion pumps (MiniMed, Northridge, CA) connected via an infusion set to a collection glass vial. Pumps were shaken continuously (30 oscillations/min, 2 cm amplitude) at 37 +/- 2 degrees C. Samples from reservoirs as well as pumped samples collected at the end of the needle, at flow rates of 0.3 U/h and 0.9 U/h, were tested to assess physical stability against insulin fibrillation and chemical stability in terms of formation of high-molecular-weight proteins (HMWP) and content of insulin. Baseline values were established by similar tests of IAsp and IGlu samples stored in the marketed glass cartridges at 5 +/- 3 degrees C during the entire study.
Results: For IGlu the physical stability against insulin fibrillation was reduced in both the reservoir and at needle end compared to baseline samples. For IAsp, physical stability increased in both the reservoir and at needle end with the exception of the reservoir sample at 0.9 U/h, which still maintained 90% physical stability compared to baseline samples. Both IAsp and IGlu retained a high proportion of native insulin; however, at the study's end, IGlu contained twice the amount of biologically inactive HMWP compared to IAsp. The overall retention of antimicrobial agents was higher in IAsp.
Conclusions: The physical stability against fibrillation was reduced for IGlu, but not for IAsp, during simulated CSII use. A higher rate of formation of biologically inactive HMWP was observed for IGlu.