How Long Should Insulin Be Used Once a Vial Is Started?

Abstract

Diabetic patients treated with insulin, whether for type 1 or type 2 diabetes, are prone to often unexplained swings in their blood glucose. These swings can vary from dangerously low to persistently high levels. Most diabetic patients, and most physicians, will adjust insulin regimens so as to avoid hypoglycemia at the expense of hyperglycemia. Among the "textbook" reasons for variable glucose responses to any given insulin regimen are 1) site of administration, 2) exercise, 3) bottles not adequately mixed before drawing the insulin (for NPH, Lente, or Ultralente), and 4) duration of treatment with insulin (1).A new insulin was marketed by Aventis Pharmaceuticals about 1 year ago, insulin glargine (Lantus). The manufacturer seemed to stress that patients not use a started bottle of this insulin for Ͼ28 days (2). Two patients of mine highlighted this point.L.K. is a 76-year-old woman with type 2 diabetes, diagnosed at 55 years of age, and treated with insulin since age 56. Her insulin regimen was changed to Lantus at night together with Novolog before meals. She monitors her blood glucose four times a day. She used a bottle of Lantus until it ran out; therefore, a bottle lasted for 2 months. Her recent HbA 1c was 7.6%. I retrospectively analyzed her home glucose readings by averaging her fasting blood glucose levels for the first 15 days of a new bottle and the last 15 days of that same bottle. The results were 137 Ϯ 20 and 187 Ϯ 13 mg/dl, respectively. E.T. is a 77-year-old man with type 1 diabetes since 29 years of age. His regimen was changed from Humulin N plus Lispro to Lantus at bedtime and Lispro before meals. He checks his blood glucose levels four times a day. He observed on his own that the last 25% of his Lantus bottle didn't seem as potent as the first 75% and questioned me about this. I asked him how long a bottle of Lantus insulin lasts for him. He told me 40 days (consistent with his dose of 25 U/day). Simple math revealed that his last 25% was past the recommended 28 days.I set out to review the available literature on insulin storage. Lilly recommends using an opened bottle of Humulin R for 4 weeks, Humalog for 4 weeks, and Humulin N for only 1 week, whether refrigerated or at room temperature. Humalog Mix 75/25, Humulin 70/ 30, and Humulin N cartridges can be used for 7-10 days (3). Novo Nordisk states that vials or cartridges of Novolog can be used for 28 days at room temperature but says nothing about how long it will last if refrigerated (4). In a private communication with a staff pharmacist at Novo Nordisk, I received the following message: "If human insulin vials that are stored under refrigeration are used beyond 30 days, the stability of human insulin vials is dependent upon a number of factors in addition to temperature [sic]. These factors include the number of injections per day, volume of insulin remaining in the vial, exposure to light, agitation, and technique used for dose preparation. The impact of these factors is difficult to measure and the health professional should advise p...

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