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Insulin administration in cats

Updated: Jan 9, 2021

The diagnosis of Diabetes in your cat may at first seem overwhelming. This article is intended to answer many of your questions.

Insulin Storage

Insulin has a limited “shelf-life” so you should stop using it before the expiration date on the bottle. Generally, it is best to store insulin in the refrigerator to make sure it retains its potency. Lantus® insulin can be kept for up to 6 months if refrigerated. If you see any color change or cloudiness in the insulin bottle, discard it and get a new bottle. Do not freeze insulin. Keep it out of direct sunlight as well.


You must know the concentration of the insulin you are using before choosing a syringe. There are two types of insulin syringes: U-40 (for insulin of the 40 units per cc concentration) and U-100 syringes (for insulin of the 100 units per cc concentration). The type of syringes used must match the insulin used. Most human insulins (Lantus® and Humulin®) are 100 units per cc while most veterinary insulins (PZI and Vetsulin) are more dilute at 40 units per cc. Insulin syringes may be purchased at Oasis Animal Hospital but many clients purchase them at the local pharmacy. One reason to consider purchasing your syringes here is that some human pharmacies don’t carry U-40 syringes. If the insulin you are prescribed is of this concentration, it is better to purchase your syringes here. While syringes are generally available over the counter, play it safe and have us give you a written prescription for syringes. Insulin purchased at a pharmacy may or may not require prescription. Insulin is considered an over-the-counter medication for humans but when it is used in pets, it is technically off-label so a prescription may be needed. Syringes come in 0.5 cc volumes and 0.3 cc volumes. The syringes are graded in units. The smaller the volume, the easier it will be to read the tiny unit gradations. We recommend the 0.3 cc size for cats as it is easier to read the gradations, especially with U-100 syringes. When drawing up the insulin, always hold the bottle vertically to avoid unnecessary bubbles in the syringe. Since insulin is being given under the skin, bubbles are not an enormous problem (as it would be with an intravenous injection) but we still want to minimize bubbles. If you get bubbles in the syringe, flick the syringe with your fingers until the bubble rises to the top and then simply push the air out of the syringe with the plunger.

Injection technique

Before injecting your pet, practice drawing up the correct amount of insulin so that you are comfortable handling the bottle and the syringes. If you have trouble reading the numbers on the syringe or if you aren’t confident you can draw up the correct amount of insulin, you may also opt for an insulin pen.

Lantus injection pen

Specific steps

feline sq injection

Method of given a cat an injection

First, feed your cat. The blood sugar of a pet who has not eaten a normal meal but receives insulin may drop to a dangerously low level. If your cat is not eating, this could indicate a need for a checkup. After your cat has eaten, you are ready to give the injection. Gently pinch the skin between the shoulders between your thumb and forefinger to create a small tent in the skin. A triangle of skin is formed. Aim your needle for the center of this triangle and stick the needle in. Sometimes use the center of the scruff, and sometimes use the loose skin towards the sides or over the shoulders. By varying the location, you avoid creating scarring or fat deposits that could interfere with insulin absorption. Do not be shy or the needle will not penetrate the thick skin in this area. Pull back slightly on the syringe plunger to be sure you do not get blood back in the syringe. If you do see blood, pull the syringe out and start over. If you do not see blood, press the plunger forward and deliver the insulin. If there is struggling or your cat escapes, or for some reason you are not sure if your pet got the entire dose of insulin, DO NOT GIVE MORE. Simply wait until the next scheduled dose.

What to Watch For:

It is not unusual for a pet’s insulin requirement to change over time. When this happens, you will notice a return in weight loss, excessive appetite, and excessive thirst and urination. This is an indicator that your cat needs a glucose curve to re-adjust the insulin dose. (credit to Dr. Wendy Brookes for some of the content of this article)

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