Immunologic and biologic evaluation of insulin degradation following prolonged storage in plastic syringes

Insulin potency during storage in plastic disposable syringes for short periods of time is a concern of diabetics as well as syringe manufacturers. Previous studies have indicated that leaching of organic materials from rubber gaskets may have cytotoxic effects. The purpose of this study was to evaluate the immunologic and radioreceptor degradation of insulin storage in commercial plastic syringes. Insulin syringes were filled with insulin and stored at 4 degrees C for 2 weeks. Immunologic potency was assessed by radioimmunoassay while biologic potency was evaluated by binding to hepatic insulin receptors. Recoverable insulin was measured on days 1, 3, 7, and 14 and compared with highly purified porcine insulin. Insulin content of samples stored in all three plastic syringes showed no statistically significant (p less than 0.05) loss of immunologic or biologic potency for 2 weeks compared with stock controls. Lente insulin gave more variability in storage in the radioimmunoassay, possibly due to settling, and was less effective in displacing labeled insulin in the radioreceptor assay. We conclude that premeasured insulin may safely be stored in plastic disposable syringes under selected conditions, especially in blind and handicapped diabetic patients, for 2 weeks.