Stability of U-500 regular insulin in prefilled syringes

To evaluate the stability of U-500 regular insulin in prefilled syringes stored under refrigeration for up to 28 days.

U-500 regular insulin was drawn up in 1 mL insulin syringes in a clean, nonsterile environment to emulate conditions of a patient's home. Samples were assayed using a stability-indicating reverse-phase high-performance liquid chromatography method immediately after preparation (day 0) and after 7, 14, 21, and 28 days under refrigeration. Before evaluation, all samples were diluted to a concentration of 40 units/mL in the starting mobile phase. Stability was determined by evaluating the percentage of the initial concentration remaining at each time point.

At least 93.3% of the initial U-500 insulin concentration remained throughout the 28-day study period, with no statistically significant changes in the amount remaining. The percent of initial concentration remained above 97% for the first 21 days of the study.

A prefilled syringe with U-500 regular insulin is stable for at least 28 days when stored under refrigeration. These data are similar to those reported for U-100 regular insulin, indicating that prefilling syringes with U-500 insulin is a safe and effective practice for patients who are unable to accurately draw up their own point-of-care doses.