It's a not uncommon reaction to 'foreign' insulin in some cats and I certainly observed it was a very pronounced effect of Caninsulin on Saoirse. (She'd nap for a little while on Lantus but was up and at 'em by +2.)
Are you BG testing? I can't recommend you do so strongly enough - even more so with Caninsulin because it typically hits hard and fast and can produce very steep drops in BG very soon after the dose is given.
It can take a little while for a kitty's body to adjust to any insulin in the very early stages of treatment. Let your vet know, keep observing very closely - especially between +2 and +10 - and record all clinical signs you observe to share with your vet and also in your posts here. If you're concerned about anything unusual contact your vets straight away - day or night. Insulin is a very powerful hormone and its action must be respected to keep our little ones safe.
It may be that the post-dose lethargy will reduce after a few days of Lila's treatment. If it persists and she spends a lot of each cycle lethargic/withdrawn/depressed it could be that the Caninsulin really disagrees with her in which case you will need to talk to your vet about a change of insulin (e.g. Lantus or Levemir) which may agree with her system better. (Not all cats get on well with all insulins.)
Mogs
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