If the sugar is 100 or so, I would not give 1U, but if it is 400, I would give 1U. It is just very strange for the glucose to be 400-500 one day after 1U and then hypoglycemic another day,
Oh lord...
It's not 'strange' around here...
Kitties have various reactions to insulin...and the bounce around like they're on pogo sticks.
I learned very early on that my vet (who recommended euthanasia btw, rather than trying to give her insulin) knew nothing whatsoever about FD. Please, for goodness sake stop relying on your vet for assistance with this disease.
It is completely treatable and your kitty can have a long and happy life - however vets know so little about FD it's not funny...they just don't get the training in school about it...and have little to no time to read updated information about treating feline diabetes...
Please read the stickies, take a deep breath and get your 'determination' hat on to help your kitty. I decided not to listen to my vet at that time, or much of what any vet has said to me since then (almost 3 years now) about Luci's diabetes. As it turned out I learned more from this group than they have time to even think about.
I don't mean to sound harsh, but my experience with vets has been less than impressive...and I do not discuss Luci's care with them when I take her in for other things (like last year she broke her foot, had her dental and labs, etc.) but other than to tell them that I am taking care of her diabetes and we're using (whatever insulin we were on at the time)...I really don't want to discuss that with them.
I do want be respectful of the vet and explain to her everything going on and reasons behind going against her rec.
I'm not disrespectful toward my vets at all...they ask, I tell them and when they say, oh bring her in for a curve, fructosamine, call me for dosing advice, etc. I just smile and say 'thank you'...and let it go at that...pay my bill and leave with my kitty...end of story.
You are PAYING her for taking care of your cat - in this respect she cannot possibly earn that money...so be kind to yourself and stop listening to your vet - on this topic anyway...