Carl asked me to stop by.
If the expiration date on the vial or pen is passed, your Lantus is no longer usable. In most cases, when you purchase Lantus, you have at least a year for the insulin to reach expiration. In all likelihood, what you've got is either unstable or just no good. You're probably going to need to wait until Monday to see your vetor go to an ER vet to get a prescription. I wouldn't freak out. Chances are this didn't happen overnight and his numbers have been up for a while.
If your cat has been OTJ for this long and you have any BG tests, the rise in BG may be an indication that there's something else going on -- some sort of infection may be brewing or your cat may need a dental. It's probably a good idea to get in to see your vet as soon as you can. Just as a precaution, I'd get some Ketostix and test for ketones especially if your cat's behavior is "off."
If the container has been opened and it's been over a year, I would definitely not use it.
