Hi Adam:

I have only been on Lantus for about 6 weeks.
I treat Lantus the same way I treated Lente and Humalog, which
usually lasted 2 weeks or a bit longer than specified. I keep it in
the fridge unless I leave the house to go shopping, visit Friends,
appts., etc. At a place with a fridge I would ask to put it in theirs.
Leaving it out of the fridge for 5 hours would be my limit. Also I
never put air into the vial. Makes it last longer plus no fussing with
bubbles.

Almost aways worked for me.