How long does insulin last in a syringe?

Look at the insert: Most Insulin syringe manufacturers discourage the practice of keeping Insulin for a prolonged period of time in the syringes specially with long acting analogs like lantus (insulin glargine). I do tell my patients that it is ok for short acting insulins to be preloaded in a syringe if you are going out to eat but no longer than 2-3 hrs.