Injecting a U40 Insulin with U100 Syringes

 

What is the difference between a U40 and a U100 syringe?

U40 syringes are made specifically to be used with a u40 insulin; and, u100 syringes are made specifically to be used with a u100 insulin.  When used in this manner, the lined markings are marked correctly to be read as a number of “units” of insulin. The line positioned at the “1”, indicates “1 unit” of that insulin.

For instance, when using a u100 syringe with a u100 insulin, the mark identified as “1” refers to a measurement of “1 unit” of the insulin.  If you inject that much insulin, as long as it is a u100 insulin, you have injected 1 unit of the insulin with this syringe.

Similarly, when using a u40 syringe with a u40 insulin, the mark identified as “1” refers to a measurement of “1 unit” of the insulin.  If you inject that much insulin, as long as it is a u40 insulin, you have injected 1 unit of the insulin with this syringe.

However, on DCI we often prefer to inject a u40 insulin with a u100 syringe; in this case, the mark identified as “1” will NOT refer to a measurement of “1 unit” of the u40 insulin!

For this reason, we should first try to understand the difference in concentration between the u40 insulins and the u100 insulins before proceeding.

What is the difference between a U40 and a U100 insulin?

A u40 insulin is prepared by the manufacturer to contain 40 units of insulin per every 1 millilitre (mL) of solution.

A u100 insulin is prepared by the manufacturer to contain 100 units of insulin per every 1 millilitre (mL) of solution.

Since 100 divided by 40 equals 2.5, a u100 insulin is 2.5 times more concentrated than a u40 insulin.  There are 2.5 times more units of insulin in a millilitre of u100 insulin than in a millilitre of u40 insulin.

One other way to think of this difference in concentration is to think of some diluted drink – for example lemon juice added to water to make lemonade.

If you add the juice of one lemon to a container, and then fill it with water, you’ll have a certain concentration of the lemon juice.  And, if you add the juice of 2½ lemons to a different container, then fill it with water, this second container will be 2.5 times more concentrated (having 2.5 times more lemon juice).  That’s the same concentration difference as when you compare a u40 insulin with a u100 insulin.

 

How do you use a 0.3 mL u100 syringe with ½ unit marks to measure out a u40 insulin?

The first thing to understand is that when using a u100 syringe to measure a u40 insulin, you should no longer think of the line by the number “1” as representing “1 unit” of insulin!  And similarly, don’t think of the line at the “2” as representing “2 units” of insulin!

In fact, don’t think of the marks as representing any number of units; instead, they represent “marks”.  There are just numbered “marks” on the u100 syringes when used with u40 insulins.

You will be given specific instructions as what “mark” to use for injecting any specific amount of insulin that you want to use.  It turns out that to inject “1 unit” of a u40 insulin, you will need to use the “2.5 mark” on a u100 syringe.  To inject “2 units”, you will need to use the “5 mark” on a u100 syringe. This is because there is a 2.5 times difference in concentration between the two insulins.

When aiming for a mark, we say to “draw to” the mark (as in, “draw to the 2.5 mark”).  Because of this, we always give you a very specific dosing scale that has both the “units” of u40 insulin, and the “draw to mark” for the u100 syringe.  We abbreviate “draw to” by using the letters “dt”.  So, “1.0u / 2.5 dt” means “to inject 1.0 unit of insulin, draw to the 2.5 mark”.

Starting Scale for all u40 insulins when using u100 syringes:

Imperial        Metric               Dose          Draw to Amount
(mg/dl) ……(mmol/L)……U40 Insulin……..U100 Syringe
151-170…………..8.3-9.4……………..0.2u………………..0.5
171-185………….9.5-10.2…………….0.4u………………..1.0
186-200………..10.3-11.1…………….0.6u………………..1.5
201-220………..11.2-12.2…………….0.8u………………..2.0
221-250………..12.3-13.8……………1.0u…………………2.5
251-290………..13.9-16.1……………1.2u…………………3.0
291-350………..16.2-19.4……………1.4u…………………3.5
351-410………..19.5-22.7……………1.6u…………………4.0
411-450………..22.8-25.0……………1.8u…………………4.5
451-500………..25.1-27.8……………2.0u…………………5.0

Please make sure that your U100 syringes are 3/10cc-0.3ml U100 syringes with half unit markings. U100 syringes also exist in other sizes and without half unit markings, and it is important to make sure that you have the right ones.

Why would we want to dose u40 insulin using 0.3 mL u100 syringes with ½ unit marks?

Using the conversion to dose U40 insulin with a 3/10cc – 0.3ml U100 syringe with half unit markings will allow you to dose accurately and consistently.

In addition, the dosing scale rung increments are small.  Notice that there are 0.2 unit increments on this u40 à u100 converted scale (shown above), rather than the routine 0.25 increments if you were to be using a u40 syringe. This is very helpful for our many cats who are particularly sensitive to insulin and small changes in the doses.

The converted scale therefore ends at the highest rung being lower overall than the standard scale (u40 syringe scale); and, this works best for many of our cats.

Your Log: Glucose Record Requires Both the Units and “DT”

When noting the dose in your log, please put both the units of insulin and the draw to amount: 1.0u / 2.5dt . Note that you do NOT put a “u” for the draw to.  Please recollect that the “dt” is just a mark that we use to deliver an amount of insulin; it is NOT the same as the number of units injected.

Make sure to check each time when you dose that you have looked at the correct DRAW TO amount. Inject the amount of insulin by using the correct DT mark.

Once you have switched to U100 syringes, please give away or keep your old U40 syringes in a completely different place: if you mix up the syringes and dose the draw to amount with your old U40 syringe, you will be dosing your cat 2.5x the amount of insulin you are trying to give.  This is extremely dangerous, as too much insulin can kill!

Please post in Introductions & Questions if you need help or more information.

 

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