Insulin in Transit
I have a pump and use Humalog. I change the cartridge every three days and have noticed a dropoff in effectiveness on day three. When I traveled to Ireland for 12 days, I decided to change the cartridge every fourth day while I was there. I increased my boluses on day four, but could never catch up with my increased glucose readings. The insulin seemed to be at a 20 to 40 percent effectiveness. Lilly or some other manufacturer must have on hand the degradation rate at different temperatures. I would assume the temperature of insulin in a pump in my pocket is somewhere between room temperature and body temperature. I realize that insulin is a complex animal, but any information would be helpful to making adjustments on day three or day four. Don McNamara
Christy Parkin, MSN, RD, CDE, responds:
Yes, insulin is a complex animal. It is a small protein that is particularly sensitive to environmental factors, especially temperature extremes. Although I do not know whether temperature was, in fact, the cause of your loss of insulin effectiveness, all of the insulin manufacturers warn against using insulin that has been exposed to temperatures higher than 86°F, either in the vial or in your insulin pump cartridge. The temperature of the insulin may exceed ambient temperature when the pump housing, cover, tubing, or sport case is exposed to sunlight or radiant heat. Another point to consider during your travels is that any unopened insulin you are carrying will need to be refrigerated at 36°F to 46°F, and not exposed to any extreme heat, cold, or light. After the vial of insulin is open, it can be used for up to 28 days. However, there may be more going on than simply changes in insulin temperature.
Travel can make blood glucose control somewhat difficult due to the body's response to changes in time zones, sleeping patterns, eating schedule, activity level, and other factors. That's why extra blood glucose monitoring is recommended during travel. Also, it is not uncommon to notice a drop in effectiveness of insulin on day 3 of pump wear, which could be a site issue or an insulin issue. Changing sites every two days can be very helpful, although I realize that changing sites more often increases the cost of your supplies.
In your case, using your cartridge for an extra day (from 3 to 4 days), combined with international travel, may have contributed to your higher blood glucose levels. The main thing to remember is that it's important to check your blood glucose frequently while you are traveling so that you can make appropriate insulin adjustments. And, again, you need to protect your insulin from extreme temperatures. If you continue to have questions about the effectiveness of your insulin, I recommend that you contact the manufacturer. In the case of Humalog, contact the Lilly Answers Center at 1-800-LillyRx (1-800-545-5979).