Converting Units Of Insulin To Milligrams And Milliliters

In our latest question and answer, the pharmacist discusses how to convert insulin units to milligrams and milliliters.

Converting Units Of Insulin To Milligrams And Milliliters
Feb 06, 2019

Peggy asked

How do you convert the Humalog insulin between units and milligrams? What about conversion to milliliters?


Insulin Title

It's incredibly uncommon to see insulin noted in milligrams (mg). The insulin products you get at the pharmacy will always be labeled in units, or as a concentration in terms of units (e.g., U100 means 100 units of insulin per 1mL of liquid).

The term 'units' refers to International Units (IU), which is a measure of the "biological activity" of a specific drug or substance. International Units are used over a conventional metric measure (such as milligrams) to make it easier to compare different forms of the same drug. Essentially, the use of International Units is a way to standardize.

For example, you may see 'Vitamin A' available as a variety of forms in 'over the counter' supplements, including:

  • Retinol
  • Beta-carotene

Although they both provide 'Vitamin A', they have different biological activities (i.e., potencies) regarding how much 'Vitamin A' they actually provide. Therefore, they have been standardized with International Units as follows:

One International Unit (IU) equals:

  • 0.3 mcg of retinol
  • 0.6 mcg of beta-carotene

In the same vein, for Vitamin E, one International Unit (IU) equals:

  • 0.67 mg of d-alpha-tocopherol
  • 0.9 mg of dl-alpha-tocopherol

Units To Milligrams Insulin Conversion

Convert Arrows

The conversion factor for human insulin is: One International Unit (IU) equals 0.0347 mg of insulin.

International Units are far easier to understand, especially when it comes to dosing, for insulin. Having a prescription say 'inject ten units' is easier to comprehend than 'inject 0.347 mg'.

Similarly, when listed as a concentration, such as the commonly used U100 (which means 100 units of insulin per 1mL), units correspond tidily with a volume (e.g., 20 units is contained in 0.2 mL).

Nevertheless, if you are so inclined to convert between units of insulin and milligrams, you can use this handy conversion tool:

Insulin: Units To Mg Tool

Type a value in any of the fields to convert between Insulin measurements:

*Note: The tool rounds to the 'hundredths' place for milligrams

Converting Insulin Milliliters To Units

While we are on the subject of converting units of insulin to milligrams, it is important to discuss a common source of confusion regarding insulin dosing, which is the relationship between milliliters and units.

Insulin products are listed in terms of a concentration, such as U100 or U500.

U40 stands for:

  • 40 Units of insulin per 1mL (milliliter)

U100 stands for:

  • 100 Units of insulin per 1mL (milliliter)

U500 stands for:

  • 500 Units of insulin per 1mL (milliliter)

So, if you have a U100 insulin product, and you need to inject 50 units, that would come out to 0.5 mL.

Similarly, if you have a U500 insulin product, and you need to inject 50 units, that would come out to 0.1 mL.

You can convert between units and mL for the most common type of insulin concentration, U100, below.

U100 Insulin to mL Converter

Type in units of U100 insulin to convert to mL:

Milliliters: 0

If you are using syringes to draw up and inject your insulin, it is vitally important to be sure you are using the correct ones to prevent dosing errors.

For example, you cannot use U100 syringes if you are utilizing a U500 insulin product. Drawing up half-way, to 0.5 mL, on a U100 syringe will equal a dose of 50 units of a U100 insulin. However, doing the same (drawing up to 0.5mL) with a U500 product would yield 250 units!

Insulin Analogs Vs. Human Insulin

Different Types Of Insulin Pens

There is also another, very important reason, why insulin products aren't listed in milligrams and that has to do with the existence of Insulin analogs.

Insulin analogs and human insulin technically use the same conversion (1 Unit = 0.0347 milligrams) and are considered 'equipotent'.

Nevertheless, there are significant differences in the pharmacokinetic profiles of each (e.g., how they are absorbed and metabolized).

Human Insulin

'Human' insulins include:

  • Regular insulin (example products include Humulin R and Novolin R).
  • NPH insulin (example products include Humulin N and Novolin N).

Regular human insulin products are considered 'fast-acting', with an onset of action around 30 minutes. High concentration regular human insulin (U500), have a slightly faster onset of action and duration of action.

NPH (Neutral Protamine Hagedorn) insulin is also known as isophane insulin and is intermediate-acting. It is regular human insulin with added zinc and protamine, which causes a delay in absorption and prolongs the duration of action.

Insulin Analogs

Insulin analogs are altered forms of insulin and are manufactured via genetic engineering. Analogs are created in such a way to alter their pharmacokinetic characteristics from human insulin.

For example, there are several 'rapid' acting insulin analogs, and have a faster onset of action than human insulin products. These include:

There are also long-acting insulin analogs, with a longer duration of action than NPH insulin. These include:

Conversions Between Human And Analog Insulin

Although all insulin products are considered 'equipotent' in regard to the fact that 1 unit of each equals 0.0347 mg, as described above, they have significant differences in their onset of action, time to peak effect, and duration of action.

Therefore, it doesn't make much sense to quantify them all in the same way in terms of their milligram strength as it could easily cause confusion and dosing errors.

Most insulin products, in their prescribing information, discuss how to convert or switch between different types, with many recommending a one-to-one conversion (with caveats).

For example, the prescribing information for Levemir (a long-acting insulin) recommends the following if you are switching from an NPH insulin:

"For patients with type 1 or type 2 diabetes on basal-bolus treatment, changing the basal insulin to LEVEMIR can be done on a unit-to-unit basis. The dose of LEVEMIR should then be adjusted to achieve glycemic targets. In some patients with type 2 diabetes, more LEVEMIR may be required than NPH insulin."

Final Words

To wrap it all up, there generally is not a need to convert between units and milligrams of insulin, but we have provided a tool if you wish to use it.

More commonly, it is necessary to convert between units and milliliters, and we have provided tools in this article to make that easy for you as well.

  • Elsevier ClinicalKey: Insulin Class Overview (Accessed 2/06/19)
  • Levemir Prescribing Information
  • Proposal to initiate a project to evaluate a candidate International Standard for Human Recombinant InsulinMethylsulfonylmethane: Applications and Safety of a Novel Dietary Supplement. World Health Organization
  • The Influence of Methylsulfonylmethane on Inflammation-Associated Cytokine Release before and following Strenuous Exercise. PubMed

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