How many units left in an empty pen?

Spent many decades scavenging every last drop of insulin out of a 1000-unit vial.

Since switching to pens about a decade ago, I’ve been able to extract anywhere from 5-15 units out of an “empty” (no more clicks) Humalog Kwik-pen with a syringe. That one or more mealtime doses for me.

It helps to blow some air in there. Recently I’ve decided that it’s easier to get the last units out with the pen with the pen pointed up instead of down. Of course it “sucks air” on the way to the last units but I’m real good at flinging bubbles to the top of a insulin syringe to push out the air.

I think… the Humalog pens in particular are always overfilled at least a little? The Tresiba pens I’ve been using seem much more precisely filled. In particular there’s rarely any need to prime more than a unit out of a new Tresiba pen. But I often have to prime 4 or 5 units of “gap” out of a Humalog Kwik-pen.

Anyone doing better than me?

I fear this is a trick question to find out which of us is the most OCD, and I’m afraid I’m going to win.

I still prefer vials and syringes for fast acting insulin. I find it more portable and worry free, fitting two bottles (Novolog and R) plus syringes that I reuse and BG meter and a few rolls of emergency smarties in a very small zipper case that fits in any front pocket. I carry that in my pants any time I am out of the house, so always ready to bolus, test BG, or treat low. I also always travel with fruit, but keep the glucose for running out of everything else, emergency use only.

I do use Tresiba in a pen, however, because I only take it first thing in the morning, so keep it by my bed or with the rest of my traveling toiletries in my leather traveling case when I’ll be staying over somewhere. I have a Timesulin cap on it, which is great for allowing me to verify that I didn’t forget my morning dose. The Timesulin cap is the main reason I haven’t changed to Tresiba in a vial, though I have considered it.

I never prime my Tresiba pen, ever. There is simply no need because I keep it stored, and always inject it, upright with the air bubble opposite the needle. So what if there is an air bubble inside - it is impossible for me to inject it, so I just ignore it.

Tresiba is in a 300 unit pen, and I use 20 units per day, so I always get 15 doses per pen. But then, when those “official” doses are done, I find there is still just barely an additional 20 units in the pen, though only about six of those could be pen-injected. Instead of wasting the remaining 14 units I extract all 20 using a syringe, still keeping the pen upright. So in fact I get 16 doses per pen, leaving it completely empty.

I use this opportunity to rotate in a new syringe, so my syringes are replaced on the same 16 day schedule.

OK, OCD enough?

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What do you mean you inject it upright? How do you do that?

Sorry that didn’t make sense. I think I should have said “always inject with the pen upright, with the needle pointed down and so that the air bubble is floating to the top and cannot be injected when the button is pressed”.

This works well because I always like to see where on my upper thigh I am injecting, so I roll on my side since I inject before getting out of bed, and have access to all of my thigh that is visible.

I’ve been injecting for almost 50 years and for the first 30 or so injected into my buttocks where I couldn’t always see where I was injecting. I found I had developed a few dense lumps which concerned me. So I changed to using visible upper thigh and after a few years those lumps all disappeared. I don’t know if it was overuse from not being able to see where I was injecting, or It could have been those early animal source insulins. But in any case I now always inject where I can see what I’m doing, so keeping pen upright occurs naturally.

I can include a pic if this still isn’t clear but hopefully that explains it.

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And one other thing in case it wasn’t clear. I install a single pen needle in a new pen and reuse it until I have injected all the units I can get from the pen (the advertised 300 units). When I remove and discard that pen needle, the pen essentially becomes a mini vial from which insulin can be extracted using a syringe, which is how I get that last 20 units.

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Thanks! Perfectly clear.

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This is my experience as well. Novolog pens are in the middle - about 3 units gap when starting out with a new one.

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I’m thinking due to manufacturing tolerances any “300-unit” pen likely has 310-315 units in it. I’ll have to actually total how many units I get out.

My mental model of the priming we have to do with a new pen, is that the “pusher rod” isn’t even in contact with the “rubber” when shipped. I guess to take into account temperature expansion/contraction.

I know for sure if I leave a needle attached to a pen (which I do all the time) and leave it in a warm car for even a few minutes that a unit or two will pop out the needle.


I too use 20 units per day Tresiba but I never get a “21st” dose out of a pen. Indeed there is always between 5-6 extra units available at the end according to the clicker. Like clockwork.

My “extra units via syringe” have always been Humalog I will try extracting from the end of a Tresiba pen soon!