Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066











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Insulin is the injectable medication you will be using 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” where blood sugar levels will be mapped out over the course of a 10-24 hour period. The curve will show if the insulin is lasting 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 (click here for more information) but if you are a beginner you may want to master giving the injections before moving on to actually taking blood samples.

Insulin is a very 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 presently four insulins commonly in use for cats: Vetsulin (also marketed as “Caninsulin®” in other countries), PZI insulin (presently available as Prozinc® insulin), Lantus® insulin (also called Glargine insulin), and Humulin (genetically engineered human insulin available in several formulations with different duration 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.

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PZI insulin
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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® insulin) became available in the end of 2009. PZI is available through compounding pharmacies but these sources do not have batch to batch quality control, meaning the relative strength from batch to batch is not predictable. While pricing may be attractive, we recommend against purchasing compounded PZI insulin and sticking to brand name.

Lantus® insulin (Glargine) was marketed for human diabetics as a “peakless” insulin, meaning that it maintains a 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.

For more information on Glargine Insulin click here.

Lantus® insulin (Glargine)
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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 in the home setting for pets. It is often used in the hospital setting to quickly reduce dangerously high blood glucoses in an emergency setting.

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.

Humulin N
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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 the formation of bubbles.




The bottle you are currently using need not be refrigerated though if you have a supply of insulin bottles, it is probably best to refrigerate the bottles that are not in use.

  • Do not use insulin that is past its expiration date. In fact, it is a good idea to change to a fresh bottle every 6-8 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.





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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 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 syringe volume, the easier it will be to read the tiny unit gradations. We recommend the 0.3cc 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.

Drawing Insulin

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INJECTION PENS(original graphic by

There are many insulin products available in pens for human use but only two products commonly used in pets: the Vetsulin VetPen and the Lantus Solostar. The Vetsulin VetPen is designed for pet use and all the benefits of the injection pen can be realized. The pen injects its insulin via a push-button mechanism which does not require as much manual dexterity as a syringe. There is also a dosing dial that allows for very accurate measurements. The pen is loaded with a cartridge which lasts several uses while a new needle tip is placed for each use. The needle tip is inserted through the pet's skin and the button is pressed. 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.

To see a video explaining the process, click here.

The Lantus Solostar is different because it was meant for human use. People require fairly large insulin doses so they go through the Lantus cartridge quickly. A cat will go through a Lantus cartridge so slowly that refrigeration is necessary to get maximum use from the cartridge. The problem is that the Lantus Solostar mechanism will not measure with accuracy if the pen is refrigerated. This means that the pen cannot be used as a pen; it must be used as an unusually shaped vial. Syringes still must be used to draw up the accurate amount of insulin from the pen.

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

To view a video guide demonstrating how to draw up insulin click here. (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 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.



As of September 1st, 2008 it has been illegal to dispose of used syringes in the regular trash even if they are in a thick plastic container. You must instead return used needles to a special needle disposal center or use a special “mail-in” sharps container. In California, medical wastes must go to special medical waste landfills.

For more information on what you are allowed to do: click here.



First, feed your cat. A pet that has not eaten a normal meal but receives insulin may drop his or her blood sugar to a dangerous low level. If your cat is not eating, this could indicate a need for a check up with your veterinarian. After the pet 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, 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 you are using a pen, simply insert the needle into the skin (be sure the needle is not in fur and is actually through the skin) and press the injection button. Leave the needle in place for a count of five before pulling it out.

Areas where insulin can be administered

Areas where insulin can be administered

Areas where insulin can be administered
(Photocredit: Teri Ann Oursler DVM)

If there is struggling or your pet 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.

Boehringer Ingelheim, the makers of Prozinc insulin, have put together a video on giving insulin to your cat. It can be viewed by clicking here. (Again, these steps would be the same for injecting any insulin.)



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.


 Page posted: 1/16/10
Page last updated: 3/12/2021