It seems strange to have the measuring unit for something be a “unit” instead of a measurement of mass. There is an agreed upon standard for what a milligram or a microgram is. Outside of the context of insulin, a “unit” is undefined and variable. Context: I’m an RN with type 1 diabetes. I understand drug concentrations and insulin dosing. This one just seems like a strange anomaly in the world of measuring medications. My only guess is that the actual hormone is so minuscule to measure that even nanograms and picograms can’t do it?
In: 264
Here is answer I was able to find:
>Historically when insulin was discovered at the turn of the 20th century by Banting and Best, they did not have the advanced technological luxury we have today to readily measure the weight of an insulin molecule. Furthermore, insulin was available in various strengths and concentrations so it was difficult to measure the mass or volume of insulin.
> Scientists in the past however were smart people and they came up with creative ways to do things. Therefore, an indirect model was used to quantify a standard amount of insulin. Like most historical scientific studies, we used animals to test a hypothesis. In the case of insulin, we used rabbits. One international unit of insulin was the amount of insulin required to lower the fasting blood sugar of a rabbit by 2.5 mmol/L. With the advanced technology nowadays, we now know one unit of insulin is equivalent to 0.0347mg of pure crystalline of insulin.
> Now is it easier to dose insulin based on 0.0347mg of insulin or 1 unit?
So it seems that 1 unit was a method of standardization used prior to our ability to more accurately calculate the amount of insulin in a sample. We couldn’t test actual concentration so instead, we standardized around an amount to produce a certain outcome. 1 unit was 1 unit, regardless of concentration, with the delivered volume being the variable.
We likely could change over to a more scientifically accurate system today, but given that most folks who take insulin are not medically minded, it would likely cause more confusion than it is worth. They know to take insulin based on units, so best to just keep that the standard.
IUs are used to measure the effectiveness of a compound. Since many compounds come in different formulations, you don’t need to bother with the mass; what you measure is the desired effect. Many vitamins (like D and A) that can be formulated in multiple ways will be measured in IUs because you’re interested in how well they do what they’re supposed to do. Importantly IUs, unlike mass units, are not comparable between things (I.e. 1000 IUs of vitamin A in no way can be compared with 1000 IUs of vitamin D).
It was a measurable amount that could easily be tested/duplicated.
One of the earliest methods was:
1 unit was the amount needed to [induce hypoglycemic seizure](https://journals.physiology.org/doi/abs/10.1152/ajplegacy.1926.76.3.677?journalCode=ajplegacy) in a 2kg rabbit (sorry for nasty/brutal part).
But, overdosing a tiny animal means it will have a small-noninsignificant effect in humans.
Once there were several types of insulin, it also helped to have relative potency (rather than a harder-to-measure and clinically arbitrary when comparing different insulins) milligram/microgram measurement.
“Units” are what scientists use to measure the effect of a certain drug when a more precise measurement of the amount of substance would be a big hassle. There are different kinds and formulations of insulin with different effectiveness. A patient doesn’t need to know the number of millimoles going into them, they want to know how much of the stuff keeps their blood sugar down.
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For drugs like insulin, that are synthetic versions of real proteins/hormones, there can be batch to batch variation when they make it. Because of the variation in manufacturing, they have to calibrate each batch to have the same efficacy per dose, and that is what an international unit (IU) is. If you used mass (mg) you’d get different effects for the same dose. Each lot of drug will have a certificate of analysis (COA) that spells out the exact calculation.
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