How to determine the correct syringe for your pet’s insulin

It's important to use the correct syringe for your pet's insulin

A syringe is a syringe, right? Actually, syringes come in different units of measure, different sizes, different needle length, different needle width, different, different, different! Giving insulin to a pet, especially if you’ve never done that before, is stressful enough without having to worry about giving the wrong dose. Unfortunately the body of an animal (or a human) is not so willing to forgive an insulin overdose. Hypoglycemia can and frequently does become life-threatening.

U100 syringe

Let’s start with the volume that the syringe holds inside of it:
Syringes can hold 1/2 cc, 1 cc, or 3/10 of a cc (total volume of insulin).
These syringes have markings of UNITS on them also.

Insulin comes as 40 units and 100 units, meaning;
40 units per 1cc OR 100 units per 1cc
20 units per 1/2 cc OR 50 units per 1/2 cc
10 units per 1/4 cc OR 25 units per 1/4 cc

(Keep in mind that 1cc = 1 ml)

Insulin comes as 40 or 100 unites per cc

This number of UNITS that the insulin is marked for is essential for the syringe to draw up the correct quantity of insulin. Insulin U40 must be used in U40 syringes. U100 insulin needs to be used in U100 syringes.

You might be thinking, “Okay I picked the right syringe for my insulin, now I’m being asked about the CCs! How do I know that?”  Before you buy any insulin it’s important to know how much insulin you need to give.

Let’s say you’re using U40 insulin and you need to give 10 units to your pet. Since U40 means 40 units per 1cc, then 10 units would mean 1/4 cc as shown above. Since you’re only giving 1/4 cc, then anything above 1/4 cc syringes would be fine. Since most people don’t like to draw insulin up to the very top of the plunger, getting a 1/2 cc syringe would work fine.

Now since you made sure that the insulin has the same designated Units (U40) as the syringes, all you have to do is draw up to the 10 units mark on the syringe to get the correct dose.

Another example: let’s say you have the U100 insulin and U100 syringes and you need to give 50 units to your pet. Since U100 means 100 units per 1 cc, then 50 units would require 1/2 cc of volume.  Sure, it’s possible to get away with using the 1/2 cc syringes but again since most people don’t like the plunger to go too high (feels like it might fall out) then using the 1cc syringe would be fine.

Now since you made sure that the insulin has the same designated Units (U100) as the syringes, all you have to do is draw up to the 50 units mark on the syringe to get the correct dose.

There are other markings on the syringe, and those have nothing to do with dose; that’s why I left those for last. Needles are marked with a gauge designation which tells you how thin the needle is– the higher the number, the thinner the needle is. For most insulin, using the highest gauge (thinnest needle) possible would provide the most comfort to your pet.

As an example to clearly visualize thickness, imagine 15 gauge would quite thick like a nail to hang a small photograph and 29 gauge (commonly used for insulin) would be so thin that it’s almost not felt at all by the pet. Just for discussion’s sake, a 22 gauge syringe is commonly used for thicker and more viscous liquids such as Adequan (for joints) or Percorten-V (for Addison’s).

As always, if for whatever reason you feel uncomfortable or need assistance with figuring the insulin dose please, please, call your veterinarian or your 1800PetMeds Pharmacist.  Getting the correct dose of insulin into your pet is extremely important.

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  1. I ordered new insulin syringes and did not realize the the difference. I used before u40 1/2 cc, the new ones are u40 1cc. Is the only difference the amount the syringe holds? It looks like a different amount would be drawn up. I only give 5cc per dose. Do they give the same dose?

  2. Hi Bobbi, as long as the syringes are both U40 and the insulin is U40 then the correct dose (in UNITS) will be drawn out. Both U40 syringes will contain the exact volume of liquid when drawing out a specific dose from a U40 insulin.

    Also in your question you said “I only give 5cc per dose” I believe you meant to say 5 units ? If you are only giving 5 units then using the 1/2 cc syringes would be easier to measure out since the volume is so small. Although the U40 1cc will also measure the same volume of insulin from the U40 product, the 1/2 cc will simply be easier to see and measure out.

  3. you didnt go into detail about the LENGTH of the needle, i’m clear on the amount i’m drawing into the needle (4cc), how to give the shot, and so on…but the pharmacist showed me there are different length needles. 1 needle tip looks like its approx 1/2″ long, 1 looks about 1/4″ long.
    BTW, I am giving a small 10# poodle insulin shots. do you have any thought on the length of needle that would be best ?

  4. We bought a different syringe it a little wider do you we the same 1 unit as the other syringe

  5. My dog has diabetes and I have been giving him 6 units of Vetsulin 40 units per mL (u-40) for dogs and cats every twelve hours with a U-40 syringes and everything was fine; but when I ran out of syringes I went to Walgreens pharmacy and they sold me a different kind of syringes their brand claiming that they are the same and that I should give him the same dose indicated in the syringes, However, something is not doing right because my dog walks very slow, has no energy and had lost a lot of weight, in spite that I feed him the same and he is eating well and hungry all the time. I am worried if I am giving him the correct doses or not. The Walgreens syringes read as follows: Super thin Syringes – Confort Assured. Use with U-100 Insulin for 50 Units or less 0.5 ml volume, 29 gauge, 1/2: (12.7 mm) needle length, 10 single-use syringes, latex free. Could you please tell me if these syringes are the same than the U40 syringes I was using? Thank you very much

  6. Those U100 syringes are not the same as the U40 syringes and should not be used with U40 insulin. You need to use U40 syringes with U40 insulin. Please take your dog to the vet for a checkup and get the correct syringes.

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