Insulin is the injectable medication you use to control your diabetic cat’s blood sugar. The goal is maintaining blood sugar levels in an acceptable range over the course of the day with once or twice a day dosing (usually twice.) 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. Alternatively, you can learn how to monitor your cat’s blood glucose levels yourself but if you are a beginner you may want to master giving the injections before moving on to taking blood samples.

Insulin is a simple molecule but it does differ slightly between species (i.e., cat insulin is different from dog insulin, which is different from human insulin). There are currently four insulins commonly in use for cats: Vetsulin (also marketed as Caninsulin® in other countries), PZI insulin (currently available as Prozinc® insulin), Lantus® insulin (also called Glargine® or Basaglar®), and Humulin (genetically engineered human insulin available in several formulations with different durations of action).

Vetsulin is of pork origin, which is handy for dogs because canine and pork insulin are identical. Vetsulin can also be used in cats, although feline insulin is closer in structure to beef insulin. Vetsulin is considered to be an intermediate-acting insulin. It is available in a vial to be used with syringes or as an injection pen, which many people find easier to use than a syringe.

PZI insulin is a long-acting insulin formerly available as a beef origin product. After its manufacturer exhausted its supply of beef pancreas it became unavailable, much to the consternation of many diabetic cat owners. Fortunately, a human origin PZI insulin (called Prozinc®) became available at the end of 2009.

Lantus® insulin (Glargine) was marketed for human diabetics as a peakless insulin, meaning that it maintains glucoses in a narrow range. It is a long-acting insulin used in humans to provide a basis for glucose control, which is then fine-tuned with short-acting insulins. Lantus has proved very effective for diabetic cats and is available at most regular drugstores.It comes in both a vial to be used with syringes or in an injection pen form. A generic called Basaglar® is also available but only as an injection pen. Recent increases in the price of glargine insulin has led to a resurgence in popularity of both Vetsulin and ProZinc insulin for cats.  Another similar human insulin called detemir (brand name Levemir®) is becoming popular.  This is also a long-acting insulin and it is available in either pen or vial formats.

Humulin was formerly available in several forms: N, L, R, and U, each with a different duration of action. Recently U and L have been discontinued.

Humulin R is fast acting and is similar to insulin secreted by one’s body. This insulin acts too fast and lasts too short a time to be useful for pets in the home setting. It is often used in the hospital setting to quickly reduce dangerously high blood glucoses in an emergency.

Humulin N is intermediate acting. These are the most commonly used forms of insulin and are usually used twice a day in pets. In general, this insulin is not long-acting enough for feline use.

It is normal for a small white layer to settle in the bottle after it has been sitting. This layer must be evenly mixed into the solution before drawing up the dose. The manufacturer of Vetsulin recommends shaking the bottle to mix, but other manufacturers prefer simply inverting the bottle gently or rolling it in one's palms so as to prevent bubbles from forming.

Storing Insulin

As insulin prices increase, it is important to take good care of the bottle you have. You do not need to refrigerate insulin, and human diabetics commonly do not refrigerate their insulin as it is less objectionable to inject room temperature insulin versus cold insulin. That said, the bottle or pen of insulin lasts a much shorter time for a human so contamination is less of a concern. Some insulins do not contain preservatives and probably should be refrigerated, so check with your veterinarian. Here are some additional principles of insulin storage.

• Do not use insulin that is past its expiration date.
  
  
• It is a good idea to change to a fresh bottle every 6 to 8 weeks. That being said, the standard in veterinary medicine is to keep it longer; 4-6 months as long as the insulin is refrigerated and not discoloured. Please consult with your veterinarian about what will work best for you and your pet. 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.

By 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®, Detemir®, Humulin®, etc.) are 100 units per cc while most veterinary insulins (PZI and Vetsulin) are more dilute at 40 units per cc.

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, the presence of bubbles is not an enormous problem (as it would be with an intravenous injection) but we still want to minimize the presence of bubbles for the sake of measurement accuracy. 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.

View a video guide demonstrating how to draw up insulin. (The video is made on behalf of Prozinc® insulin, but the procedures are the same for any of the insulin vials.)

Used syringes or pen needles 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. Special containers can be purchased for needle disposal or the used syringes can be returned to the veterinary hospital for disposal if you prefer.

By Injection Pens

The pen injects its insulin via a push-button mechanism that does not require as much manual dexterity as a syringe. There is also a dosing dial that allows for accurate measurements. The VetPen is loaded with a cartridge that lasts several uses while a new needle tip is placed for each use. Fresh insulin cartridges are available to reload the pen. Human pens are fully disposable so when the cartridge of insulin runs out, the pen is discarded and a new pen is used.

Insert the needle tip through the pet's skin and press the button. The needle should stay in place under the skin for a few moments (the manufacturer recommends counting to 5) so that all the insulin dose can be expressed from the pen. If a human pen is being used, you will need to get special longer needle tips as the short human needles tips may not penetrate animal skin properly.

This video explains the VetPen process.

Disposing Needles

Used syringes or pen needles should be placed inside a thick plastic container (such as a liquid laundry detergent bottle or similar receptacle.). If the needle is in such a container, the entire container can be closed up and disposed of in the regular trash at home. Special containers can be purchased for needle disposal or the used syringes can be returned to the veterinary hospital for disposal if you prefer.

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.

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. Photo by Dr. Teri Ann Oursler

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.

Giving insulin. Photo by Dr. Teri Ann Oursler

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.

The manufacturer of Prozinc insulin put together a video on giving insulin to your cat. (Again, these steps would be the same for injecting any insulin.)

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 pet needs a glucose curve to re-adjust the insulin dose.

Be clear on how to recognize hypoglycemia (listlessness, incoordination, potentially even seizures or collapse). If you are suspicious of this problem and the cat is relatively subtly affected, simply feed an irresistible meal. Be sure you have Karo syrup, nutrical gel or some other sugar source for your cat in case it becomes necessary to drizzle some in the cat's mouth. See Diabetes Overview page for a review of this concept.

Learn more about Glargine insulin.

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