Don’t put a pen back in the fridge once you’ve started using it, this is against manufacturers advise as per the leaflet - I think the big change in temperature from warm room to cold fridge will negatively effect the insulin - so it won’t work the same
It is against the advice, though the advice on my Novorapid leaflet has no particular emphasis on this point (IMO - your opinion may differ from mine), so I assume it's simply down to a lack of testing rather than that the insulin will change in any way. I quote: "Novorapid(R) Penfill(R) that is being used or carried as a spare is not to be kept in the refrigerator. You can carry it with you and keep it at room temperature (below 30degC) for up to 4 weeks."
Certainly when abroad somewhere hot I will put my pens back into a fridge (if available) rather than risking them getting hot in a room without my realising, I also have no problem injecting from a new vial that's just come out of the fridge (though it feels a bit odd
).
You have to interpret the rules as you see fit, I'd be interested to know if there is some sort of scientific basis for not placing in-use insulin back in the fridge though.