Hi Denise! Happy to see you over here from the Facebook group!
One thing you'll need to try to understand about Lantus....it's a "depot" insulin...when it's first started, it usually takes 5-7 days before you're going to see the full effect of the dose you're giving.
Here's the "technical" jargon:
After you inject it into your subcutaneous tissue, the acidic solution is neutralized by your body to a neutral pH. Because glargine is not soluble at a neutral pH, it precipitates out into a form that's not soluble in subcutaneous fat, and there forms a relatively insoluble depot. From that pool, or depot, of precipitated glargine in the tissues, small amounts slowly move back into solution over time and then to the bloodstream.
In simpler terms, when you first start, only a little goes "to work"....the rest goes into the "depot" and slowly releases into the bloodstream. But until the "depot" is completely full, it can't "release" an amount in relationship to the dose...so it will take several days before the depot will release the entire dose over the 12 hour cycle.
3U is a really high starting dose. Lantus has a formula for the starting dose that's Weight (in kgs) x .25....so unless Mr. F weighs about 30lbs, 3U is way too much. If you choose to continue giving that much, please keep a close eye on him and test as much as possible. Make sure you also have a
"hypo kit" ready in case you need it.
We've seen lots of cats here that were started out at too high a dose and they ended up in an ER (or worse) due to severe hypoglycemia.
High numbers make us worry, but they take time to do damage....it's the low numbers that kill quickly.