Does Insulin Lose Its Punch?
I am on the Medtronic MiniMed Paradigm pump, and I've noticed that my insulin is not as effective toward the end of the MiniMed reservoir. I believe this happens in conjunction with the end of the vial of insulin I draw from as well. Is this common? I use insulin glulisine (Apidra), and I never use a vial that is more than 30 days old. I use approximately 60 to 70 units per day. I fill the MiniMed reservoir with 210 units when I replace the insulin. John Dorney, Franklin, New Jersey
Belinda Childs, MN, ARNP, BC-ADM, CDE, responds: Insulin sometimes does not seem as "potent" near the end of a pump reservoir, or even near the end of a vial. The Food and Drug Administration has approved the use of insulin that is in a reservoir for up to six days, depending on the brand of insulin.
The studies that determined this time frame were based on how insulin worked in a controlled setting. Insulin's effectiveness in the day-to-day life of the average person with diabetes certainly varies from the lab result, though, and it varies even more from individual to individual. This is part of what makes diabetes so complicated: Everyone is different.
If you are using 210 units every three days, you would use a vial of insulin about every 12 days. Sometimes people use insulin from more than one vial, which prolongs the exposure to outside factors. If possible, use insulin out of only one vial: That way, you will use it up in a timely manner.
It also may be helpful to look at how you store insulin. Do you keep it in a cool, dry place? Any insulin you have not begun using should be stored in the refrigerator. Protect insulin and other medications from sun, temperatures higher than 86 degrees, and, most of all, humidity. Keeping them in a warm, humid bathroom, or in a sunny area of the kitchen, is not advisable.
Your problem may be due not to your insulin but to your pump site. Look at your pump set-up and site-change process. Are you reusing the reservoirs? If so, this may contribute to the insulin's growing ineffectiveness. Does your insulin act differently depending on where your infusion site is? Are you rotating pump sites so that you don't use the same half-dollar-sized areas over and over? Sometimes, as it gets close to time for a needle change, insulin absorption may slow. Living with diabetes often requires the skills of a good detective. You will have to explore these different possibilities and consult with your doctor if you cannot find a solution or your problem starts to significantly affect your blood glucose control.