Hello and welcome. Sounds like you've got a good background knowledge to help Feen.
Basaglar is a biosimilar to Lantus/glargine, so also a good choice. Yes, you dose every 12 hours with cats. Sorry to hear your vet is so out of date with diabetes. The
AAHA 2018 Guidelines for Managing Diabetes with 2022 update mention both Lantus/glargine and Prozinc as the recommended choices for cat, twice a day.
Feen eats wet food, used to eat FF but she has me transitioning to DM canned.
There is nothing special about DM. It is just overpriced with not great ingredients. It's OK for diabetics, though many grow tired of it. It is called dietetic management, not diabetic management because they were no longer allowed to call it diabetic management. Any low carb food, what we consider 10% and under to be, is fine to feed. This includes some of the Fancy Feast pates etc. This
food chart has a list of some of the more common ones available in North America.
What type of glucometer do you have? What were the indications feed was diabetic? Any other conditions present? We like people to put certain information in their signature as that info impacts what we suggest. Details on what goes in the signature an how to start a spreadsheet to share kitty blood sugar data in here:
New? How You Can Help Us Help You!
We ask that people have their signature and spreadsheets set up before posting in the Lantus forum.
As for starting dose, we have a couple dosing methods we use with Lantus. One (Start Low Go Slow) says 0.5 units if on an all low carb wet food diet. The other, the Tight Regulatio Protocol, is 0.25 units per kg of ideal weight of cat, which would be about 1 unit with Feen. More details on the dosing methods are here:
Dosing Methods: Start Low, Go Slow (SLGS) & Tight Regulation (TR)