Well, I promised a few weeks ago to perform this test, so here goes. We froze some Humalog for two weeks in our home freezer. After thawing, the insulin looked clear and normal in appearance.
After letting it come to room temperature for a few days, we performed the test we will now affectionately refer to as the “Reeses Peanut Butter Incident”.
We injected 3 units of the frozen/thawed Humalog and waited for 40 minutes. His blood glucose as measured by finger stick was as follows:
Prior to Injection - 87
40 minutes after injection - 87
Injested the peanut butter cups
50 minutes after eating 153
2 hours 30 minutes after eating 144
His afternoon insulin to carb ratio is 1:12. I have included a gratuitous picture of the test components and his CGM tracing. Please note, this sensor has run consistently 30-40 mg/dl high, so the 200 shown is actually 153 as measured by finger stick.
Conclusion - Freezing insulin doesn’t destroy it as I thought, but it dramatically changes the activity profile. It actually handled the 36 carbs, although not nearly as quickly as we would like. Also, it is surviving in his system longer than expected. We ate a known dinner 3.5 hours after injecting the insulin, and now 4.5 hours after injecting, he is going low, almost as if this test dose stacked on top of his dinner dose even though it was taken a long time before dinner.
It goes without saying, don’t try this at home, this was one test done in isolation on a willing subject, [Well bribed subject, but hey 3 peanut butter cups looks pretty good]. It has given me a belief that Humalog is more robust than I had been led to believe, although the unusual action curve is a little spooky.