Dosing U40 insulin with 3/10cc-0.3ml U100 syringes with half unit markings

 

Please note that the information here refers to information for dosing U40 insulin with U100 syringes:  

NEVER dose U100 insulin using U40 syringes – you will be dosing your cat 2.5x more insulin than you think and will be putting your cat in danger.

Using U40 insulin with U100 syringes

 

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

The numbers following the “U” refer to the percentage of insulin in one standard unit of liquid: U40 insulin is 40% insulin (and 60% solution); U100 insulin is 100% insulin (and 0% solution).

U40 insulin is diluted vs. U100 insulin that is pure insulin.

The next step can be a little difficult to understand – please post in Introductions & Questions if you need more explanations;
1 unit of insulin (not 1u of liquid, but 1u insulin) is the same regardless of the concentration.

As U40 insulin is diluted and only 40% insulin, to end up at a full 1 unit of insulin, you need 2.5x the volume of total liquid.

• 1st unit of liquid : 0.4u insulin
• 2nd unit of liquid: 0.4u insulin
• ½ unit of liquid:    0.2u insulin
TOTAL: 1.0u insulin

One other way to think of things is to think of some diluted drink – for example a gin and tonic (to use a somewhat universally known drink – you can substitute a Ribena and water for the UK, a kir – the cassis vs. the white wine for France.. a pastis (the anisette vs. the water) in southern Europe .. etc ).

(Please note that the following is simply to illustrate and that we are not condoning or suggesting drinking gin & tonics, kirs or pastis in order to test what follows!)

If you fill a glass with 40 ml of gin and 60 ml of tonic : your glass will contain a total of 100ml of liquid….

But to drink 100 ml of gin you will need to drink 2 ½ glasses of the mix of 40ml gin/60 ml tonic: the 40ml + 40 ml + ½ 40 ml or 20 ml = 100 ml gin (and 250 ml of that mix of gin and tonic in the process).

That is like U40 insulin.

On the other hand rather than drinking 250ml of a mix of gin and tonic you can also simply fill your glass with 100ml of gin and drink that.

That is like U100 insulin.

In both cases you will have drunk 100ml of gin.

The unit markings on U40 syringes take into account the “250ml (2.5u) of gin & tonic” to have 100ml (1u) of gin.

On the other hand, the one unit line on a U100 syringe is 1.0 units of liquid that is 100% insulin so equal to 1.0 units of insulin…. The equivalent of that 100ml of pure gin with no tonic.

 

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Why use a conversion and dose U40 insulin with U100 syringes?

While from time to time a U40 syringe with half unit markings will appear on the market, in general, U40 syringes are only available with full unit markings.

Without the half unit lines it is very difficult to dose ¼ unit increments (0.25u, 0.75u for example) accurately and consistently…. And it is even more difficult, if not impossible, to dose fat unit increments (0.25u fat…) with any consistency at all.

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, because of the way the conversion scale is set up, the scale doses are lower, which can be helpful for cats particularly sensitive to insulin/to small changes in the amount of insulin:

 • The “usual” scale goes up by 0.25u increments: 0.25u, 0.50u, 0.75u….. 1.0u is reached on the 4th rung of the scale.
• In order to allow you to dose on the lines of the 3/10cc-0.3ml U100 syringe with half markings, the “convertible” scale goes up by 0.20u increments: 0.20u, 0.40u, 0.60u… 1.0u is reached on the 5th rung of the scale.

The convertible scale is therefore lower than the standard scale.

The conversion

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 (please see the insulin syringe sticky in the Knowledge Centre for more information).

To dose U40 insulin with the 3/10cc-0.3ml U100 syringes you need to draw 2.5x the dose of insulin you are giving into the U100 syringes: for example, to dose 1u of insulin, you need to draw the insulin to the 2.5 unit line marked on the U100 syringe. (Please look at the graphic above again to understand why).

In this example, the dose of insulin you are giving remains 1.0u (not 2.5u) – to measure that 1.0u you need to draw to the 2.5u line on the U100 syringe: that is simply the way you are measuring 1.0u of your U40 insulin.

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 as again, it is simply how you are measuring the dose, it is not the number of units you are dosing.

Please make sure to double check each time that you dose that you have looked at the right DRAW amount.

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.

Convertible Starting Scale for dosing U40 PZI (ProZinc, U40 US/Canadian Bovine PZI) or Caninsulin/Vetuslin with 3/10cc-0.3ml U100 syringes with half unit markings

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

 

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