A survey of Storage Temperature of In-use Human Insulins at Patients’ Homes and Analysis of Their Stabilities under the Simulated Highest Temperature Identified in the Patients’ Home

Abstract

Objectives: To obtain patients’ household storage temperature of in-use human insulins, and to determine stability of human insulins under the simulated highest home storage temperature. Methods: Out-patients with diabetes (N = 47) who received either regular insulin (RI), isophane (NPH) or premixed RI/NPH insulins, used with a self-assembly pen were given a temperature logger to track storage temperature of in-use insulins for a consecutive 5-7 days. The highest and lowest storage temperatures were identified. Times per day the temperature being outside the recommended storage ranges were reported. Determination of the stability followed the analysis in the United State Pharmacopoeia (42^nd ed.). Three batches of each insulin above were stored in temperature controlled cabinet under the isothermal highest home storage temperature identified previously. The assay for insulin content was performed at a weekly interval for 4 weeks, and was reported as percentage label amount, of which 95-105% was considered as passed. Physical changes were also observed. Results: Of the patients keeping insulin in a refrigerator (n = 22), 18 had temperatures outside the recommended 2 to 8^๐C range, with the average times amounted to 8 hours 30 minutes per day. The temperature was above 30^๐C for all patients reporting keeping insulin at room temperature, with the average times corresponding to 7 hours 57 minutes per day. The highest storage temperature identified was 43.6 ^๐C. At the simulated isothermal 42±2^๐C, RI, NPH, and premixed  RI/NPH insulins had insulin contents in the 95-105% range up to 2, 3, and 4 weeks, respectively. No significant physical changes were observed except an increase in viscosity of NPH and the premixed. Conclusions: Home storage temperatures of insulins were mostly out of the recommended ranges for about one-third of times in a day. Under isothermal temperature of 42±2 ^°C, RI, NPH, and RI/NPH insulins retained their acceptable potency at 2, 3, and 4 week, respectively.