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Correct way to give an injection when "tenting" the skin. This makes sure the insulin is injected into the skin flap created by "tenting" it. When the skin "tent" is released, the injected insulin is under it, or subcutaneous.


Close-up illustration of a syringe needle showing bevel, point and heel.

Syringes [1] are commonly used to inject pets with insulin. The strength of an insulin is measured in International Units (IUs). [2] The two common strengths are U40 and U100, meaning 40 units and 100 units per millilitre, respectively. Cubic centimeters (cc's) and milliliters (mL's) are interchangable, so syringes marked 1ml equals 1cc; 0.5 ml equals 1/2cc. 3/10cc equals 0.3ml. [3]

There are U100 Syringes designed for use with U100 insulin and U40 Syringes designed for use with U40 insulin. They were at one time color-coded: U100 syringes having orange caps while U40's have red ones. [4] Unfortunately some U40's now have orange caps, too -- check the barrel carefully for U40 or U100 to be sure!

See Syringe parts for a breakdown of the parts of a syringe.

Syringe useEdit

NeedleBevels svg

This shows the common bevels for syringe needles. The one used on insulin syringes and insulin pen needles is the one at the top-standard bevel.


Wrong way to give a shot: The needle has totally passed through the "tented skin". The insulin, or any other injected drug, will be injected into the air. Note that in this graphic, the injection point is much closer to the "pinch" area holding the "tent" up. In the correct graphic, the injection point is closer to the body.

To inject, pull skin up first, and insert the needle firmly parallel to the body, bevel side up. [5]

Insulin syringes are intended for a single use only. Using them twice [6] may contaminate and/or interfere with some insulin's activity, in addition to wearing the protective coating off the needle and causing more pain at injection. [7] When the protective silicon coating is worn away by re-use, it can also contaminate the insulin; white precipitates [8][9] can form in the vial from the silicon, possibly interfering with the action of the insulin. [10][11]

Insulin syringe needles. Image 1, never used. Image 2, used once. Image 3, used twice. Image 4, used six times.

You can also see that when the needle is held with the bevel side up (facing toward you, not the patient), the bevel is angled to slide under the skin, meaning less pain at injection.[12] Comparing the first use and the sixth use in the photo examples, you can see how the coating has almost been totally worn off by the sixth use. You can also see the point beginning to blunt after first use. When a needle becomes blunted from re-use as you see in the photos, it can create lipohypertrophy due to skin damage. [13] Injecting insulin into areas like this means poor or slow insulin absorption. Some people use yesterday's syringe or disposable needle as a lancet, though.

If you should bend a needle while drawing insulin, discard the syringe and start again; don't try to straighten it out. [14] Inserting the needle all the way into the vial makes it less easy to bend. [15]

Injection HelpersEdit

  • If you feel all thumbs when giving shots or think you need more than two hands when giving them, Palco's Inject-Ease may be just what you need. The device holds a filled BD insulin syringe (Micro-Fine or Ultra-Fine BD brands). Inject-Ease inserts the needle into the skin and delivers the injection at the touch of a button. [16][17][18] It's a big help with both small children and pets needing insulin shots. It has been used with success for some CDMB dogs who were difficult at injection time. BD shows the Inject-Ease on their syringes page for dogs. [4]
  • Magni-Guide [19] by BD, is both magnifies the syringe barrel scale markings and can help steady the vial and syringe while drawing insulin. The device is designed to work with Lilly insulin vials. One can use Sanofi-Aventis (Lantus, Apidra) insulins with it, but the fit is loose so the vial must be assisted by the user's hands; Novo Nordisk vials also fit Magni-Guide, but very tightly--they may even crack the device.

Drawing InsulinEdit

  • Do NOT wipe the needle with alcohol as it removes the protective coating. This coating is what makes injection easier and less painful. [20]
  • To eliminate bubbles: If drawing insulin from a vial, set the syringe plunger to the dosage you want to draw, put the needle into the top of the vial while the vial is still upright, and push all the air out of the syringe. This will maintain air pressure equilibrium in the vial once you draw the dose and, because the vial is upright, will not cause air bubbles to mix with the solution. Turn the vial upside down and draw the insulin slowly.
  • If you do get air bubbles into the syringe, it's ok with most insulins to re-inject the insulin into the vial and draw again until the air is gone. [14] Check that this is ok with your insulin. See also injecting insulin. Slower draw is less likely to draw bubbles.
  • Another way to get rid of syringe air bubbles is to hold the syringe upright and give it a tap or two with your finger. The problem with having air bubbles in the injection is that you will not be getting the full dose of insulin; the bubbles take the place of it. [21]
  • Some people prefer to gently jiggle their vials to make any air bubbles rise to the top, away from where the needle will draw. [22]
  • Some caregivers find that certain syringe brands are less susceptible to air bubbles than others because they have a smoother push and pull motion. If you consistently have problems with air bubbles, consider trying other syringe brands.

See the Drawing insulin page for photos and more tips.

Measuring doseEdit


Right and wrong way to measure insulin units in a syringe. Using the back section of the rubber plunger as a guide will result in underdosing; the rubber plunger is solid-the drawn insulin is only in front of it. Measure from the front section of the plunger--the one closest to the needle area.

Some people find that dose differences as small as 0.1 units make a difference. Since a cat or small dog weighs 1/10 what a human does, it may easily be the case. If 0.2 units and 0.3 units actually seem to give a different result in your cat or small dog, you may find it useful to try half-unit marked syringes. This guide shows how to read fine doses of 0.1 through 0.5 units. [23]

  • For very fine doses (less than half a unit increments), some people have tried:
    • Using a magnifier.
    • Diluting the insulin (this must be done with the correct diluent and usually is done by a pharmacist.)
    • Using a U100 syringe with U40 insulin and converting (see Conversion below).
    • Experimenting with the size of droplets they can coax from a syringe, learning those sizes, and measuring them against fractional unit sizes.
    • Learning to eyeball fine doses down to 0.1 units [23].
    • Plungers may be pushed or pulled with a "screwing" motion for finer control of partial units.

Dead SpaceEdit

Needle and hub

Needle and hub.

Some syringes for other uses have detachable needle hubs, but insulin syringes have theirs permanently attached. When they were reusable and made of glass, there was sometimes a problem with "dead space"-the area where the needle and its hub fit onto the syringe. It was common for this area to hold insulin that wasn't being injected when the shot was given. [24][25][26][27]

When you use only one insulin for injection with a syringe, the dead space can leave you slightly underdosed as this amount of insulin was still in the syringe when it was discarded, and also a waste of insulin.

But when someone was using two insulins in the same syringe, the situation could be just the opposite. [28] The dead space insulin from the fast-acting insulin that's drawn first would then be returned to you when the slower-acting insulin was drawn, so you'd be getting a slight overdose of your faster-acting insulin. It was capable of causing hypoglycemia for some people. [29]

The dead space made it difficult to accurately measure the real number of insulin units, as the amount of it would vary from syringe to syringe when used for injections. [30]

The advent of plastic disposable insulin syringes that allowed the needle to be directly attached to the syringe barrel put an end to the dilemma. If you look carefully at syringe specifications, you'll see they all claim either a low or no dead space. [31][32][33][34][35][36] This means less dosage variability-more accuracy and continuity-from injection to injection whether you use one insulin or two in a syringe.

Needle pluggingEdit

A needle can become plugged for more than one reason. If the syringe was prefilled and not stored with the needle pointing upward, the insulin can settle in the downward pointing needle. [37] Two of the three insulins in the Lente family--Lente and Ultralente--contain the largest insulin crystals. Ultralente crystals are desctibed by the British Pharmacopia as, "Majority of crystals having a maximum diameter greater than 10 m.". [38] Lente insulin is comprised of 70% Ultralente insulin and 30% Semilente insulin, so the majority of the insulin in a Lente vial is Ultralente, with the large insulin crystals.

It only makes sense then that the finer the gauge of an insulin syringe needle, the more chance there may be for needle plugging--the larger Ultralente insulin crystals plugging the injection needle. [39] Monotard was a Lente R-DNA insulin made by Novo Nordisk; Novo also produced this product under the name Novolin L. Eli Lilly produced equivalent insulins under many names, including Humulin L. At one time, both companies produced this type of insulin in beef, pork, and in mixed beef/pork forms. We see that the British medical journal, The Lancet, had an article about Monotard and needle plugging in July of 1978, [40] and that two other Lancet articles followed it within a short period of time. [41][42]

If the larger, longer-acting Ultralente crystals which is 70% of Lente insulin never make it under the skin, what does would be the shorter-acting Semilente insulin along with the insulin's excipients. It would be much like not resuspending the insulin properly; the insulin is not going to work as it should. A shared personal experience came from someone who has used beef Lente insulin as his basal for more than 50 years; he does not use any needle gauge finer than 29, nor any needle length shorter than 12.7 mm/1/2" for his beef Lente insulin injections. His reason was to avoid the possibility of the Ultralente crystals of the insulin from remaining caught in the needle. A similar reasoning may be behind the AAHA's recommendation of using syringes with the standard 12.7mm/1/2" length and 29 gauge needles. [43]

Drawing insulin from a pen or cartridge to a syringeEdit

Pen cartridge with a syringeEdit

  • If you need more precise doses than a pen provides, you must use a syringe. Many penfill cartridges can be used with syringes, [23] just like small vials, but often require that you inject a similar volume of air into the cartridge every time you draw insulin. Once you've used a syringe on a cartridge, that cartridge should not be reinserted into a pen.

Disposable pen with a syringeEdit

  • If you are stuck with a disposable pen (e.g. Novo Nordisk's Flexpen), and need the extra precision of a syringe, things get a little tricker. You must inject extra air BEFORE you draw out the insulin.
  • Fill the syringe with air, empty it into the pen, then (with pen above syringe), suck the same amount of insulin back out. Do it this way whether you're transferring to a vial, extracting 1ml at a time, or just using the pen every day as a vial.
  • Here's why -- as you remove the insulin from the Flexpen, the pressure inside the cartridge will drop, which will pull on the pen's screw-and-plunger mechanism, which doesn't expect to be pulled. (Just pushed).
  • Eventually, the screw-and-plunger will break, possibly contaminating the insulin. So you must try to keep the pressure inside the pen about neutral or a bit positive (pushing back on the screw).
  • Finally, don't ever try actually using the Flexpen again as a pen once you've begun this process! It is practically guaranteed to break eventually. Possibly spectacularly.
  • Using a pen some days, and a syringe other days, has caused problems for some users. The dosages on the pen are not exactly the same as those shown on the syringe. If you must do it, keep one pen for syringe use, and another for pen use, and mark them clearly.

Prefilling tipsEdit

There are times when you may want to prefill a syringe with a known dose and leave it for yourself or someone else to use later. If doing so, keep in mind:

  • Recap the needle with great care -- needles can easily go through the side of the cap into your fingers.
  • Store the recapped needle point-up to avoid clogging the needle.
  • If the insulin needs refrigeration normally, so do the prefilled syringes.
  • The "cloudy" insulins (NPH, Lente/Ultralente, PZI, Mixes) need to be re-suspended before use. Gently roll the syringe back and forth in your hands as with the vial. Improperly suspended insulin may lose some or all of its effectiveness.
  • Some insulins, including Lantus and Vetsulin, will react with the syringe's inner coating over time and lose effectiveness, or even lose their time-delay action. Check with your insulin manufacturer if prefilling syringes is permitted.
  • According to Novo Nordisk, [44] prefilled syringes containing any of their Novolin, Actrapid, Insulatard, Actraphane, and Mixtard insulins can be kept refrigerated for 30 days. Eli Lilly says any of their Humulin insulins in prefilled syringes are good for 21 days when refrigerated.

Buying syringesEdit

U100 BrandsEdit

Common brands of U100 syringes are BD [45] and Monoject.[46]

  • The Children With Diabetes page link below[47] has links to syringe brand comparisons.
  • The page linked below [48] gives an overview of all BD syringe types with clickable photos that enlarge.
  • Wal-Mart [49] has a house brand of syringes, ReliOn, that compare to BD syringes in everything except price. [50] The page below [51]  has a clickable photo that enlarges for better comparison of the BD syringe and the ReliOn. [52] Wal-Mart also has ReliOn branded insulins, which are now made for them by Eli Lilly. The only difference here also is in the price.
  • Precision Sure-Dose syringes are made by Terumo, [53][54] marketed by Abbott. They compare favorably to BD, but cost quite a bit less. The link below [55] describes all available models and has a clickable photo that enlarges for a better look. [56] CVS pharmacies in the US stock and offer Precision syringes.
  • Ulti-Care [57] offers U100 syringes with barrel sizes 3/10 cc (no 1/2 unit markings), 1/2 cc, and 1 cc with a variety of needle gauges from 28-31. Its 28 and 29 gauge syringes have a 1/2" needle while its 30 and 31 gauge syringes have a 5/16" needle. Factoring in shipping, the prices are about equal to buying syringes offline. No prescription is needed to purchase syringes from UltiCare; it is located in Minnesota where no state law requires it. Shipping within the US only.
  • Comparison chart showing all types of U100 insulin syringes sold in the US. [58]

Retailers on-lineEdit

  • [59] offers a broad range of U100 syringes at reasonable prices. Shipping within the US only.
  • Diabetic Promotions [60] offers another large selection of syringes and supplies, and will ship to Canada and worldwide.

U40 BrandsEdit

The two most common brands of U40 syringes available in the US are Vetsulin and UltiCare. [61] Either brand may be obtained at your vet's or through ordering online. No prescription is needed to purchase syringes from UltiCare; it is located in Minnesota where no state law requires it.

Outside of the US, Caninsulin syringes and BD syringes for use with U40 insulin are available.

Prescription LawsEdit

Some countries require a prescription [62] for insulin syringes and/or pen needles.

In the US, whether or not you need a prescription for syringes/pen needles is determined by state, not US, law. The laws of your state will apply re: syringes/pen needles requiring a prescription. If you order syringes or pen needles online, the law of the state where you're ordering them from will apply. If you order from a business whose state does not require a prescription for syringes or pen needles, you will not need one, even if the laws of your state of residence says you do. Conversely, if you live in a state where there's no mandatory prescription for syringes or pen needles and order from a company in a state where a prescription is necessary, you will need one to do business with them.

Any pharmacy may have its own policy regarding a prescription being necessary or not. [63] It's best to ask before you place an online order if the store's policies aren't clearly stated or make a trip to the brick and mortar pharmacy.


U100syringe U40insulin

Use of U-40 insulin in U-100 syringes. Top syringe is a 3/10 cc (maximum 30 units) syringe with half-scale (half unit) markings. Bottom syringe is a 3/10 cc (maximum 30 units) syringe with no half-scale (half unit) markings.

Though it's not recommended by veterinarians, some caregivers use a U100 syringe with a U40 insulin. That requires “converting” the U40 concentration to a U100 strength. [64] See the conversion table. If you choose to use the U100 syringes for U40 insulin, a fast way to calculate the right amount of units is to multiply the number of U40 units given by 2.5.

The advantage of doing this conversion is the possibility of greater precision for low-dose animals -- precise dose increments of 0.2 units are possible with half-unit marked U100 syringes (if your insulin is U40). On the other hand, if you find the conversion confusing, it's best not to try -- it can be extremely dangerous to get this math wrong.

Syringe disposalEdit

You should dispose of syringes and other "sharps," like lancets, in accordance with your local, state or provincial, or national laws. Consult your trash company, your local or state/provincial health department, or your vet or pharmacist for that information. In some places, sharps have to be disposed of as "medical waste." Some people take them to the vet or pharmacy for such disposal--whether required to by law or not--although that may involve a fee. In other places, there are no specific requirements. You can seal them in a plastic container (such an empty laundry detergent or soda bottle), mark them as sharps, and put them in the regular trash. Some pharmacies also carry sharps containers for about $3-$5 in the US. This page link below [66] has links to additional information under the heading "Needle Disposal." I16

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More InformationEdit

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