Wil Dubois

Got questions about life with diabetes? So do we! That's why we offer our weekly diabetes advice column, Ask D'Mine, hosted by veteran type 1, diabetes author Wil Dubois in New Mexico.

Confused about converting various units to get insulin dosing right? Wil's got your back today.


{Got your own questions? Email us at AskDMine@diabetesmine.com}


Michael, type 2 from Maryland, asks: Can you please help me? I have been on Lantus Solostar pens, now switching to Toujeo 300. I had a supply of my old Lantus to use up before I started on the Toujeo. My Question is: Currently I take 68 mL of Lantus Solostar. How much must I now use of my new Toujeo Solostar 300? According to my calculations I only need to take 34 units of Toujeo. Is this correct? My endocrinologist has left the practice and when I called them they said that I should use the same quantity of Toujeo, which does not make sense to me.

Wil@Ask D’Mine answers: Yes. No. Maybe. OK, everybody take a deep breath here. Then go get a cup of coffee. It’s Math in the Morning with Wil.

But before we get into that math, we have a few linguistic problems to straighten out. You say you take 68 milliliters of insulin. I don’t think so. At least not from a Lantus Solostar pen. How do I know that? Because it’s not possible. The damn pen only holds 3 mL in the first place! To take 68 mL, you’d need to inject twenty-two and a half pens.

If you were using that much insulin your insurance company would put out a “hit” on you just to keep themselves from going bankrupt. Not to mention the effects on your body.

Take no offense. I’m not making fun of you. We all know that diabetes math gets easily confusing, and most type 2s unfortunately don’t get access to enough diabetes education, even when they go on insulin. Why is that? Well, partly it’s insurance coverage, but largely it’s because many docs think you have the “simple” kind of diabetes and don’t need any education. Ha! There is no “simple” diabetes, and we all need as much diabetes education as we can get. So I’m delighted that you wrote me.

Now, what the heck is going on here?

Here’s the deal: If you are dialing up your pen to “68” you are taking 68 units of insulin, not 68 milliliters. Units and milliliters are very, very, very different things, and—as you’ll soon see—the difference plays a key roll in the confusion about what to do about injecting a concentrated insulin like Toujeo.

Buckle up, here we go with the metrics lesson...

A milliliter is a measure of liquid volume that is 1/1000th of a liter, or about the volume of 20 drops of rain. An old-fashioned insulin vial holds 10 mL of fluid, about two teaspoon’s worth if you ripped the top off and poured it out. Please don’t. That would be like pouring expensive French Perfume on the floor. Meanwhile most pens hold 3 mL, less than a teaspoon (although the Toujeo pen only holds 1.5 mL). Those darn pens don’t hold as much as they look like they do!

A unit, on the other hand, is a measure of how much insulin is packed into each milliliter of the fluid in the vial or pen. Officially, one unit is defined at the biological equivalent of 34.7 micrograms of pure crystalline insulin, a measure that comes from the dawn of insulin, and just happens to be the amount required to induce hypoglycemia in a rabbit (don’t ask). But never mind all of that. For our purposes we’ll be OK with just knowing that units are the number of insulin particles crammed into a given volume of fluid, or put another way, how concentrated the insulin is.

Because, and many folks don’t know this, there are many flavors of insulin:

  • Pet insulin is usually U-40, so 40 bits of insulin in each mL
  • Insulin for people over the last few decades has been U-100, or 100 bits of insulin in each mL, but there’s also a U-500 for really insulin-resistant folks. At one time there was also a U-80
  • The higher the number, the stronger the action of the insulin because there are more insulin bits per drop

Back in the days before pens, different concentrations of insulin required totally different syringes. As you can imagine there were mistakes, sometimes with tragic consequences, and this is one of the reasons that for a long time insulin was standardized at U-100. But then two things happened: We got pens and we got fat. 

A fatter population needs either more insulin, or a more powerful insulin; and a pen should eliminate the dosing confusion, but as you yourself have experienced, it doesn’t. More on that in a moment.

OK, so Toujeo is a U-300 insulin. That means it’s three times more powerful than the U-100 Lantus. Which means you should take 1/3 of your old dose, right? (I’m not sure how you came up with your number of half your old dose, but it doesn’t matter as you’ll soon see.)


The makers of Toujeo and the FDA have tricked you to try to make your life easier. To reduce the risk of errors, like those that were seen in the olden days, the pens for concentrated insulins like Toujeo deliver a smaller volume at each click. So 30 “units” on the dial from a Toujeo pen is a lot less fluid than 30 “units” on the dial from a Lantus pen. The idea is to have patients always use the same number, regardless of the medicine used.

Basically, they’ve torn up the hypo-bunny unit rule and replaced it with what is really just a relative number. Instead of units, they probably should have renamed them something like “dose equivalent” or “insulin scale” or even something fun like “sugar bopper number.” Because what we now have are fake units, not something scientific. Something more like the scale on a Sleep Number Bed. If you get a comfy night’s sleep at "30," that’s all you need to know. The tension of the springs or the PSI of the air bags is irrelevant.

By redefining the unit, it doesn’t matter what pen you use. The idea is that you'll always set the darn thing at the same number. Run out of Toujeo and need to borrow some Lantus from a friend to tide you over? Just dial up your regular dose and the pen delivers the right amount of medicine. The idea here is to keep it simple for us. The problem is that we’re smarter than the FDA and Big Pharma think we are. We get it that a U-300 is more powerful than a U-100 one. We therefore think we should take less, when really the new pens are already delivering less for us.

I think that once we can get our heads around the new system, it will work well for everyone.

Except, well, damn it, it didn’t work out as planned. At least, not for Toujeo.

Because Toujeo, even though it is really just three-times concentrated Lantus, doesn’t quite work three times as well. Even the manufacturer’s prescribing data says, “For patients controlled on Lantus expect that a higher daily dose of Toujeo will be needed to maintain the same level of glycemic control.” 

So in the trenches, this is how it works: Let’s say the 68 units (not mL) does a great job for you. Your A1C is in the sweet spot, your overnight and morning numbers are low, and you only have hypos during jazzercise. The endo now puts you on this new magic juice, which unlike Lantus is still under patent protection. But now you need, oh let’s say... 82 units to keep controlled, because even though the numbers have been fudged to be the same, the medicine doesn’t work as well.

WTF? What the hell was the point? You’re now taking even more insulin, right? No. No you’re not. Remember that it’s all smoke and mirrors when it comes to the units at this point. Toujeo is a concentrated insulin, with more units squeezed into each milliliter, so at each sugar bopper number you’re actually injecting less fluid. This is a good thing, as the body doesn’t like large amounts of fluid injected under its skin. So even though the U-300 Toujeo isn’t really three times stronger than the U-100 Lantus, and it seems like you have to take more, you still come out waaaaay ahead in terms of how many milliliters of fluid you’re actually injecting.

Goodness! That was a long answer to your question, huh? But the endo’s office was more or less correct. Just take the same dose (which is not the same quantity, using their words), at least to start. Of course, you won’t really be taking the same. When you set your dial to 68 units, you’ll be getting something more like 68 one-third units of a more concentrated insulin.

Hopefully, this all makes some sense to you now. We just need to teach ourselves that even though we all “know” the dose isn’t the same, we still need to dial up the same number.


This is not a medical advice column. We are PWDs freely and openly sharing the wisdom of our collected experiences — our been-there-done-that knowledge from the trenches. But we are not MDs, RNs, NPs, PAs, CDEs, or partridges in pear trees. Bottom line: we are only a small part of your total prescription. You still need the professional advice, treatment, and care of a licensed medical professional.