How can I give U-40 Insulin using a U-100 Insulin syringe?

Our question this week was:

Dr. Debra – I have a cat that is a diabetic and is getting U-40 insulin but all I have is a U-100 syringe. It is 8 pm on Sunday night and the pharmacy is close. Is it possible to convert this so I can give my kitty 5 units of insulin? I need to give 5 units of U-40 insulin and all I have is U-100 syringes.


Betty R. Providence, RI


Hi – thanks for your email Betty. Let's back up a second just to make sure you understand the U-100 and U-40 labels. We have an article on this that also deals with conversions and I'll give you some of this information here.

Insulin is available in a variety of strengths – commonly referred to as U-100 or U-40. A "U" is a unit. The numbers 40 or 100 refer to how much insulin (the number of units) is in a set volume of fluid – which in this case is one milliliter. For example, U-100 has 100 units per milliliter and U-40 has 40 units per milliliter. So…U-100 insulin is more concentrated. There is essentially 2 ½ times more insulin in a milliliter as compared to U-40.

To go with the different insulins, there are different insulin syringes that match the insulin. Some syringes are U-40 and others are U-100. It is important to use the right syringe with the right insulin to achieve the correct dosage of insulin. Your veterinarian should prescribe syringes and insulin that match. The bottle and the syringes each should indicate if they are U-100 or U-40. Again, make sure they match.

It is possible to "convert" and mix and match the insulin syringes. Using non-matching equipment is not ideal and should only be done after consulting with your veterinarian and confirming the "dose" and what equipment you have (it is ideal to have someone double check you and your math – this is no place for experiments or errors!).
If you want to give 2 units of U-40 insulin in a U-100 syringe – you will need to give 5 units in the U-100 syringe.

For a full conversion chart go to: How to Convert U-100 and U-40 Insulin and Syringes.

A couple more articles that might be useful are:

Diabetes in Cats
How to Give Your Cat Injectable Medicine

Best of luck!

Dr. Debra

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