Hi Lu Lu and welcome to the forum. it is not unusual for a cat on pred to get steroid induced diabetes.
You will need to give your cat insulin and hopefully he will go into remission. Cats that have steroid induced diabetes can go into remission. But you need to get your kitty onto a low carb wet food such as fancy feast pate food. Look for foods that have 10% or less carbs. Dry food is high carb and nor recommended for diabetic cats.
Offer you kitty a low carb meal before the dose of insulin and then give 2 snacks of low carb food in the next 6 hours during both cycles (12 hours) each day and night.
FOOD CHART
I would also recommend you look into hometesting the blood glucose as that is the only way you will be able to ensure your kitty stays safe and is getting the correct insulin dose.
HOMETESTING LINK
you can a buy a human test meter at Walmart called a ReliOn Prime for $9 and 100 test strips for $17.88. You will also need a box of 100 lancets to prick the ear….ask for 26 or 28 gauge lancets. Also some cotton rounds to hold behind the ear as you test and to hold the ear afterwards.
With testing the blood glucose (BG)you need to
test, feed then give the dose of insulin in that order. If the BG is under 200 stall, don’t feed and test again in 20 minutes to see if it is rising….and post and ask for help. Change the subject line to let us know you need help.
Once you have giving the insulin, if you can get another BG test around the +4 to +7 mark, that will tell us how low the dose is taking your kitty and if it is the correct dose.
HELP US HELP YOU has the links to the spreadsheet, signature and hypo kit.
If you have any trouble settling out the SS let me know and someone will help you.
Keep asking questions. It is stressful in the beginning but we are here to help you.