Insulin Gone South?

I’m wondering if anyone has had a similar experience with insulin as have I: toward the end of a bottle of insulin, it starts to lose its effectiveness. I am very careful to only use a bottle for 28 days and then discard it. But towards the end of that period, right before I start a new reservoir for my Medtronic pump, my blood glucose goes up. Anyone else have this experience?

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Hey @Denise0730, which insulin are you using, and how long does a reservoir last for you?

Our experience with Humalog doesn’t match yours, but there are many factors at play here. For instance my son keeps an entire semester’s of insulin sitting at room temp in his dorm room with no issues. We have had some issues when he was younger and a reservoir lasted for 6 days, but I think a lot of that had to do with the insulin interacting with the plastic in his Tandem reservoir.

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Hi Chris. Thanks for the reply. I use Novolog because it is reported to be a tad more temperature stable, which is important in the southern California summers, where I live. I store my insulin in our wine fridge because its easier to prevent the insulin from getting too cold and it doesn’t take up needed space in the fridge’s vegetable drawers. I use only about eleven units of insulin per day. (I was born with only one kidney, so my body isn’t producing as many anti-insulin chemicals.) i believe the reservoir holds 300 units, but I only fill it with about 50 units—some extra just in case of earthquake or some other disaster. I’ve been Type 1 for over 55 years.


I consider switching from Fiasp to Novolog quite frequently. Think I will give it a try but am not quite sure about the transition. Very insulin sensitive, even after 50 years!

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I have observed the same phenomena for several years. It is easier to notice if you consider your TIR for the week/pump refill. I am on a Medtronic, 3 ml cart, and observed this for both Humalog and Novalog. The first and second refill ( 6days) my dex readings are 83% TIR. The third pump fill around 12- 13 days after opening a bottle the activity seems less, and TIR drops to about 60%. If I inject the insulin it seems active (a crude test of activity. It does not matter if the vial is refrigerated between pump refills or not.

I have termed this premature expiration of an open bottle of insulin. It appears similar to insulin resistance, as well as a site going bad. I get my insulin quarterly, and have had no issues with the pharmacy or time refrigerated. It would be good to know if this is just a pumpers phenomena, or if MDI see it also.


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