Five Steps to Regulation:
Step 1. Start at a low dose of PZI, Lantus, or Levemir insulin, as recommended by your vet. (Note: Humulin and Novolin Lente and Ultralente, two insulins with good track records in cats, have been discontinued by the manufacturers.) A conservative starting dose is 1.0-2.0 units, twice per day. If your cat’s blood glucose was less than 400 mg/dl (22.1 mmol/L) at diagnosis, or if your cat is on a low-carbohydrate diet, the starting dose should be only 0.5-1.0 units twice per day. Fast-acting insulins such as Humulin Regular, Humulin 70/30, and Humulin N (NPH) are not suitable starting insulins for cats, in the experience of FDMB members because of the high risk of hypoglycemia; Humulin N may be appropriate later on if you discover that longer-acting insulins cause problems for your cat. Vetsulin, also known as Caninsulin, is less harsh than Humulin N, but still appears to carry a risk of hypoglycemia, particularly for cats who are not meal-fed high-carbohydrate food, so please be aware of the risks.
Step 2. Don’t increase the dose until your cat has been on it for at least a week. If you have reason to be concerned about hypoglycemia, or if your cat won’t eat, do decrease the dose and contact your vet. Do test your cat’s urine frequently during the regulation process using Ketostix or Ketodiastix, and contact your vet immediately if the cat tests positive for ketones. Do be consistent in the timing and type of food. Do give the shots at about the same time every day.
Step 3. After 1-2 weeks at a given dose, you or your vet should perform a serial blood glucose curve (blood glucose tests every 2 hours, starting at shot time and continuing until the next shot). Follow the cat’s normal feeding schedule during the curve. The curve should be evaluated by someone experienced at interpreting feline blood glucose curves, in order to check for signs of rebound and other possible problems. If no rebound is present, follow these guidelines for dose adjustment (smaller adjustments may be appropriate for cats on PZI or Lantus):
a) If the lowest point of the curve is above 150 mg/dl (8.3 mmol/L), increase the dose by 0.5 unit.
b) If the lowest point of the curve is between 90 and 149 mg/dl (5.0 and 8.2 mmol/L), keep the dose the same.
c) If the lowest point of the curve is below 90 mg/dl (5.0 mmol/L), decrease the dose by 0.5 unit.
Step 4. Repeat the cycle of curving and waiting 1-2 weeks. As your cat’s blood glucose begins to fall mostly in the desired range [lowest point of the curve approaching 100 mg/dl (5.5 mmol/L) and pre-shot value around or below 300 mg/dl (16.6 mmol/L)], do lengthen the waiting time between dose increases. If you decide to change another factor (e.g., diet or other medications), don’t increase the insulin dose until the other change is complete (but do decrease the dose if your cat's glucose numbers consistently fall below 90 mg/dl (5.0 mmol/L) as a result of the change). Don’t be tempted to rush the process along by increasing the dose more quickly or in larger increments-- no matter how high your cat’s blood glucose is! Rushing towards regulation will cost you time in the long run, because you may shoot past the right dose.
Step 5. Once you can no longer increase the dose without the cat dropping below 90 mg/dl (5.0 mmol/L) at the lowest point, evaluate the duration of the insulin’s action. If your cat’s preshot blood glucose values are still consistently above 350 mg/dl (19.3 mmol/L), or if your cat’s blood glucose usually returns to preshot values more than an hour before the next shot is due, ask your vet about longer-duration insulins or possible adjustments to your cat’s food or feeding schedule.
