Hi and welcome to FDMB Hilvermore20. Gabapentin can make a kitty wobbly, but if this continues it may be neuropathy (weak back legs due to high BG levels). Getting the cat's blood sugar regulated is the most important treatment, but a B-12 supplement:
Zobaline (Methylcobalamin - aka - methyl B-12) helps a great deal. You can read about it here.
Congratulations on home testing, that's one of the best ways to keep your cat safe and see how the insulin is working.
Would you take a little time and create the signature and set up the spreadsheet so we can see your kitty's information each time you post?
1. Setting up your signature (light grey text under a post). Here's how:
click on your name in the upper right corner of this page
click on "signature" in the menu that drops down
type the following in the box that opens: kitty's name/age/date of diabetes diagnosis/insulin you're using and dosage amount /glucose meter you're using/what (s)he eats/any other meds or health issues (s)he has. You can add your name, and a geographic location (sometimes the country/time zone matters) Be sure to SAVE when you are finished.
2. Another thing that will help us help you now that you are BG testing at home is to set up a spreadsheet like the one we use here. You will see how the trends and patterns emerge, and members can review his/her progress before offering suggestions or advice:
http://www.felinediabetes.com/FDMB/threads/fdmb-spreadsheet-instructions.130337/
http://www.felinediabetes.com/FDMB/threads/understanding-the-spreadsheet-grid.156606/
You can read about Lantus and how it works
HERE. There is a lot of information, but you can post in that forum for help understanding, asking questions etc. The Main Forum here is mainly for issues, questions and concerns with diet, testing, other general concerns.
Best wishes to you and your kitty, I'm very glad you are here to learn, help your cat, and join our community.