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Insulin Administration in Cats

By Wendy C. Brooks, DVM, DipABVP 
Educational Director, VeterinaryPartner.com

Insulin is the injectable medication you use to control your diabetic cat’s blood sugar. The goal is dosing once or twice a day - usually twice – to maintain blood sugar levels in an acceptable range over the course of the day. Keeping the sugars in the proper range will control the excessive urination and appetite that your cat suffers from, and it will require some trial and error experimentation to get the correct dose. A dose will be selected based on what research has shown to be a good starting point, and after a couple of weeks your cat will return for a glucose curve in which blood sugar levels will be mapped out over the course of a 10 to 24 hour period. The curve will show if the insulin lasts long enough and if the dose should be raised, lowered, or kept the same.

It is normal for a small white layer to settle in the bottle after it has been sitting. When getting ready to use the bottle, roll the bottle in your palms to mix in this layer. Do not shake the bottle.

Be sure you understand the dose of insulin you are to use.
Do not alter the dose on your own.

Storing Insulin

The bottle of insulin should be refrigerated.

  • Do not use insulin that is past its expiration date. In fact, it is a good idea to change to a fresh bottle every 6 to 8 weeks. Lantus® insulin can be kept for up to 6 months if refrigerated. Regardless of whether the insulin is refrigerated, any color alteration could indicate contamination and if this is seen, the bottle should be discarded.
  • Do not use insulin that has been frozen. Insulin is not normally frozen but accidents happen, especially in smaller refrigerators.
  • Do not expose insulin to direct light or heat.

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.

Photo by Dr. Wendy Brooks

Insulin syringes may be available through your veterinarian’s office or through your regular drugstore but do not be surprised if a prescription is needed from your drugstore. Insulin purchased at the drugstore 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 prescription may be needed.

Insulin syringes are made extra fine so that human diabetics will not feel them. Veterinary syringes are similarly fine and your pet should not object to injections.

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.

Before injecting your pet, practice drawing up the correct amount of insulin
and feel comfortable handling the bottle and the syringes.

Used syringes should be placed inside a thick plastic container, such as a liquid laundry detergent bottle or similar receptacle. If the needle is enclosed in such a container, the entire container can be closed up and disposed of in the regular trash at home. Specific containers can be purchased for needle disposal or the used syringes can be returned to the veterinary hospital for disposal.
How to Give the Injections

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 with your veterinarian. After your cat has eaten, you are ready to give the injection.
Pull up a handful of your pet’s scruff. A triangle of skin is formed. Aim your needle for the center of this triangle and stick the needle in. The photos here show the injection given straight in the scruff but you actually want to vary the location with subsequent injections: 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.

Photo courtesy of Wendy Brooks, DVM
Photo courtesy of Wendy Brooks, DVM

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.

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