I know the manufacturer says that once opened, the Humalog pen should NOT be refrigerated. But I am wondering if refrigeration will cause any harm to it? Why can’t we keep it in the fridge? I refrigerate Novolin R vial all the time without any ill effect.
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Won’t hurt it at all.
In fact, it’s almost impossible to hurt Humalog. 
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Welcome, @Catalyst5 !
It will do absolutely no harm for your pen to be refrigerated after it is open. I am guessing the purpose or the mfg’s recommendation is to make sure that your insulin is at ambient temperature when you inject it: a little more comfortable, and less likely to feel the injection.
Do be aware that insulin is quite robust and can withstand a lot more than what is normally assumed. We have a lot if threads on FUD discussing many such examples.
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Thank you so much for the info! The reason that I ask is that it seems to be taking longer to see the effect of it. Instead of waiting for 25 min before eating, now we need to wait longer like 30 -35 min. So I thought maybe it is affected by refrigeration…
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Could it be that it is getting closer to the end of honeymoon? When was your child diagnosed?
Btw, we have many parents of T1s here. My son was diagnosed at 11 about 3 years ago.
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We re-refrigerate and haven’t noticed any difference honestly. Also, our pre-bolus times vary from week to week depending on activity, but 25 min - 30 minutes is the same to me. 25 minutes to 60 minutes would be a noticeable change. We just prebolus and try to wait until we get a downward trend before serving dinner. This is for when my son is over 100. If he is under 100 we bolus, wait a bit and then eat and don’t worry about it so much.
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My son was diagnosed Dec, 2017. It is possible that he is nearing the end of honeymoon. I also notice that his late afternoon numbers tend to rise more often. Morning and early afternoon before 4pm are generally stable. But after 4pm without any food or stress, it climbs up by 20-30 points.
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That’s a good tip. We just started using Libre sensor two weeks ago, so now we can use it to track the downward trend. I will try that. Thank you!
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