Re: 5/20 pmps 421+1=391 +5=301 increase tonight. 1.25 to 1.
hmmm, once a vial has been used the first time, most people have found that they will last 6 months or less, depending on how it was cared for (if it was kept refrigerated and not contaminated, for example). The expiration date is only applicable until you begin to use the bottle. You probably don't have any idea when it was initially used, do you?
Was the bottle repackaged by the vet? There is a picture here of a repackaged vial:
http://www.felinediabetes.com/FDMB/viewtopic.php?f=9&t=151
did you watch the video on how to draw up insulin doses? it's on the "care/storage of insulin" sticky that i linked just above. one of the important cautions is to not see-saw the dose back and forth between the syringe and the vial. the syringes have a lubricant in the barrel so that the plunger will move smoothly, and that lubricant doesn't belong in the insulin itself.
i get allergy shots and the nurse always see-saws the dose in and out of the vial - it drives me crazy. I asked her a while ago about it and she'd never heard anything about not doing that. she still does it. the reason i'm mentioning this is because i wonder if your vet/vet tech might've done that and it might have affected the insulin. My guess is that syringes back when didn't have a lubricant and those who learned a while ago may never have heard any cautions about it. Or perhaps Lantus is more sensitive to that than other products that get injected. i don't know. Often when we wonder about the efficacy of the insulin, people will try a new vial/pen while keeping the old one in the fridge. if the numbers don't change, we know it isn't the insulin. Often there isn't a difference after switching to a new vial/pen, but sometimes there is. It's one thing to consider when things seem to be atypical.
Would you hold your vial up to a light and see if it is at all cloudy or has threads or floaters in it? it should look exactly like water, completely clear, absolutely nothing visible in it.
Maybe just keep it in the back of your mind as something to consider checking on later. If we don't see a response from the increase in dose this time, it might be worth getting a single pen from a pharmacy to see if that makes a difference. There is a Lantus savings card that can be used
http://www.lantus.com/sign-up/offers (your cat is 18 when you register) and some pharmacies will open a box of pens and sell you just one. There's no rhyme or reason for who will break open a box and sell just one pen - you have to make calls and ask. i found a Save-on pharmacy inside a grocery store chain that would sell me one at a time.
If your vial was repackaged, i would take it back to the vet and tell him it's not good and ask for your money back.