Insulin Administration for Cats

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Insulin 101


First of all, you need to know what type of insulin your cat is receiving. Lantus (glargine) and Levemir (detemir) are increasingly common insulins prescribed by veterinarians with current knowledge of feline diabetes. Some vets will still try to prescribe Humulin N. Do NOT use this type of insulin as it has unpredicatable results in cats. PZI is still used some although it is being phased out. Vetsulin is not the best choice for your cat. You need to be aware of the type of insulin you are using and you need to know its concentration, listed in units (U). The concentration, in the United States, is most often U-40 but some insulins are manufactured in U-100 concentration.  To give the proper dose, the syringes you use must match the concentration of the insulin.  To be sure you get the right syringe, take your insulin (or the insulin box) into your pharmacist when you go to buy syringes and the pharmacist will make sure you get the right syringes.  When you buy the next batch of syringes, take the syringe packaging with you to make sure you buy the right type.

If for some reason you must use a U-40 syringe for a U-100 insulin, or vice versa, use our conversion chart.


Always make sure your cat eats around the time (up to one hour before injection) of the insulin administration. This will insure that the cat has food in her stomach (and rising blood glucose levels as a result) to counteract the action of the insulin. Also, it is often easier to give the injection while your cat is eating. If your cat is having trouble with vomiting, be very careful and watch for possible hypoglycemic episodes. If your cat is not eating, consider skipping the insulin. Remember, if your cat does not eat for 24 hours, you should take her to the vet.


This is highly recommended with all insulin use and can be done at home or at the veterinarian's office. highly recommends home-testing of blood glucose levels with a glucometer for the best care of your cat, with periodic tests by your vet, including some of the "long-term control" tests such as fructosamine (best) and hemoglobin A1c (less accurate in cats). Urine monitoring can also be done but gives a less precise indication of glucose levels and also reflects a delay of the glucose level by hours. Home-testing with a glucometer is precise and "real-time" and will greatly assist you in regulating your cat and dramatically decrease the chance of a hypoglycemic (extremely low blood sugar) episode. It is important to know when the insulin peaks (causes the lowest, or nadir, blood glucose reading) because the time of the nadir varies from cat to cat and also depends on such things as  associated illnesses, food intake and exercise.  General guidelines for insulin peaks and nadirs in humans are available on many manufacturers' web sites (see references, below).   

Knowing the peak action time of the insulin is very important because you do not want your cat to have a hypoglycemic episode that is potentially fatal.  Also, you cannot adjust a dosage on a preinjection glucose level alone. Even if the blood glucose level is high before the injection is given, the level can still drop to hypoglycemic levels after injection.   Consistently high pre-injection glucose levels can also mean a rebound affect from the insulin causing dangerously low nadirs.  If you don't know the nadir level of glucose, you may be tempted to increase the insulin dosage based on the pre-injection levels.  This would be incorrect because then the nadir level would go even lower.  Do not adjust insulin dosages without your veterinarian's approval and without knowing ALL the data.   

An excellent protocol for home testing, although specifically for glargine (Lantus) and detemir (Levemir) insulins, is found in .pdf form on this site in the Health Articles. There are other protocols listed in the same section.


Your cat should have been started on a very low dose of insulin, 1-2 U per dose, twice a day. Make only 0.5 to 1 U adjustments to your cat's dose when indicated. Although short-term reactions to insulin are quick, it still takes time (wait at least a week) for the cat's body to fully adjust to a new insulin dose.  This can be complicated by changes in diet, exercise, and any associated illnesses. Reducing carbohydrates in the diet is a POTENT factor in reducing blood sugars, and it should not be done without also reducing insulin, and careful monitoring. Go slow (unless you obviously need to DECREASE a dose to prevent a hypoglycemic episode) and make one change in your cat's routine at a time.


Do not blindly accept glucose readings as correct. Just because your cat's blood glucose levels are in a "normal range," he may still be symptomatic.  Note the cat's gait, the water intake and amount of urination, the weight.  Your cat may need glucose levels that are higher (or even lower) than "ideal." Work with your vet and make sure you get at least annual exams that include a full blood workup, including a fructosamine level.


Current recommendations from the Association of Feline Practitioners is to get a fructosamine or A1c test every 6 months if regulated, every 3 months if not regulated.  You and your vet working together will best determine the frequency of your cat's visits to the vet.  Diabetes affects many organs, so function of the kidneys, liver, heart, etc. must be done periodically, at least once per year. Your cat can get other diseases besides diabetes and regular checkups can help in early diagnosis for optimum treatment.  Home tests are becoming available for fructosamine and A1c but you still need to go to your vet for a full blood workup once a year.


You need to keep a source of simple sugars (glucose, fructose, dextrose, etc.) on hand in the case of an apparent hypoglycemic reaction.  Karo syrup, honey, and molasses are cheap sources of simple sugar and readily available and inexpensive.  If you suspect a hypoglycemic reaction, immediately rub the syrup on the gums or inside of the cheek. Do not inject the sugar into the mouth. If the cat is unconscious or having seizures, be very careful not to give too much at once as this can cause choking and aspiration.  In this case, you must be extra cautious in administration and get to an emergency vet immediately.

Don't worry about your cat's glucose going too high in this event.  High blood glucose levels (hyperglycemia) for a short period will not harm your cat.  Conversely, hypoglycemia can kill and kill quickly.  Forget the mess, forget checking blood sugar levels.  Rub a sugar syrup on the gums, and repeat even if you are on your way to the ER. We highly recommend printing out this emergency hypoglycemia sheet generously provided by Melissa, a long time contributor to this site.

8. FOOD and TREATS  

Get to know the "glycemic index" of food and treats. The glycemic index indicates effects on blood sugar, with high glycemic index foods causing rapid and high elevations of the blood glucose. Many semi-moist foods and also milk can cause big spikes in blood glucose levels.  You will want to avoid these foods and treats during the regulation period and use them sparingly afterward.  8. KNOW YOUR CAT. There may come a time when kitty does not want to eat what s/he is supposed to. It is important to know what foods you can give to entice eating, as it is crucial for the cat to eat while on insulin! Also, if you are curving and kitty's numbers start dropping too low before and/or during peak, it is lifesaving to know what to give in order to start increasing numbers. Things that have worked for myself and others: vanilla ice cream, gravy, white bread, Catsip, donuts, popcorn, dry cat food or dry cat food with tuna water dumped on it, semi-moist cat treats. You will want to know beforehand what high carb foods your cat loves, and will readily eat, so that should you find yourself in a situation where your kitty's numbers are going too low, you already have a supply on hand, and won't waste precious moments experimenting with different foods.

9. "START LOW GO SLOW". This is a popular saying on the Feline Diabetes Message Board.  Of course, you want to get your cat regulated quickly (especially for your sake!!) but if you start too high, you greatly increase the risk of hypoglycemia and also prolong the time it will take to get your cat regulated. Many people have found that ˝ a unit BID or 1 unit BID ends up being the perfect dosage to keep kitty in the 100-300 range.  If your cat requires high dosages of insulin, she needs to be checked for other illnesses and have her diet evaluated. The Cornell University Feline Health Center defines excessively high insulin doses are those greater than one to two units of insulin per pound per day. Felines who use more insulin than this should be evaluated more intensively. Other diseases may be underlying or complicating the diabetes mellitus and as a result, necessitate high insulin dosages. Problems with insulin injection, poor absorption or too rapid metabolism of insulin, or even insulin overdose are potential causes of an apparently excessive insulin requirement.

10. GET SUPPORT.  The best place for almost immediate support for your pet's health is the Feline Diabetes Message Board.  Often, you will get immediate replies to your questions.   Develop a good relationship with your veterinarian and make sure you know where to take your cat for emergency treatment.  Find neighbors, older school kids, relatives, and pet sitters who will learn about feline diabetes and give insulin injections.  A lot of people may be reluctant at first, but I've always found plenty of back-up support.

Don't get discouraged!  Thousands of us take care of cats with diabetes.  You can, too.


American Association of Feline Practitioners,

Cornell Feline Health Center,

Feline Diabetes Dictionary, 2004,

Feline Diabetes Education,

Feline Diabetes Message Board,

Glycemic Index, Rick Mendosa,

Human Insulin Time Activity Profiles,

Updated November 2009

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