Hi Brandie and Nutz!
What was his number when he got his shot? You said it was 421 at the vet? And only 46 four hours after his shot, at which time you gave him dinner? I don't want to alarm you, but 46 is very low, especially only 4 hours after his shot. If you hadn't fed him just then, he could have gone dangerously lower. "Normal" for a cat is 50-120. Usually the low point of an insulin cycle is about 6 hours after the shot, although every cat is different, and some kitties reach that point (nadir) earlier or later than 6 hours from the shot.
We need to understand your schedule so his numbers will make sense to us...
He should be getting a shot every twelve hours, give or take a few minutes. And he should be eating a meal at shot time. The way we normally do it is we test just before feeding, then we let them eat, and then we give the shot. The whole process can take maybe 10 minutes?
The other concern is that dose. Four units is huge. Most of us started out at 1 unit, twice a day. That's what my sugar cat Bob got. Now, he went as high as 4 units twice a day, but that was weeks later. He was on the same insulin, compounded PZI, for about 10 weeks. His last shot was in July of this past year, and he's been controlled just by diet since then.
I looked in your thread on Health a few minutes ago, and you mentioned that tomorrow you would not be home after his morning meal and shot? Then please definitely don't give him 4 units. If at all possible, test him before breakfast and post your number here. Lots of people are on between 6-8 AM eastern, and then some are on a few hours later. You're in WA if I remember right? What time, your time, would shot time be in the morning. I'm just trying to make sure that you can give him his insulin safely in the morning and not have to worry about him while you are at work.
We're also going to have to help you set up a spreadsheet to keep track of his test results, which is a really powerful tool in treating diabetes.
Welcome to our little group!
Carl