Don't Waste a Drop!
Here’s what I do to get all of the insulin from a pen or pen cartridge. This works on all the pen cartridges I’ve tried, and should work on all disposable pens too:
Use a syringe for the last dose in the pen.
First, if you are using a refillable pen, remove the almost empty cartridge from the pen. Then wipe the rubber stopper with an alcohol swab.
Before you insert the syringe into the cartridge, draw in some air, about 10 or 15 units. Insert into the rubbers stopper where you normally would put your pen tip needle. Inject the air. If this is done on a pen cartridge, you will see the stopper move up. Don’t worry about it. Now insert a pencil into the other end of the cartridge tube and gently push the rubber stopper back down slowly, with your syringe on the bottom and the pencil on the top. Gravity will ensure that the syringe is filled with insulin when you do this if you hold it correctly.
If you are doing this on a disposable pen, you don’t need to worry about the rubber stopper moving, as it can’t.
Next, draw the rest of the insulin out by pulling down on the syringe plunger.
This allows you to draw out all of the leftover insulin. You should be able to get out all but a couple of drops. If you tilt the pen just right, you can get it all.
Set aside with the syringe still in the cartridge so it stays clean.
Next, insert a new penfil cartridge into the empty pen, (or if using a disposable pen, get a new one out). Wipe down the rubber stopper with an alcohol swab.
Remove the needle of the syringe from the old cartridgte and do an air shot to get out all of the air and or bubbles, then insert your syringe into the new pen (instead of attaching a pen tip needle). Dial up the rest of your dose, and inject these remaining units into your syringe. I usually add one extra unit. Remove the syringe from the pen tip, do an air shot to make sure you have no air bubbles (this is where you need the extra unit) and then you can proceed to do your shot.
I usually use up all of my insulin this way, and end up getting a few extra units out of each penfil cartridge.
This works with disposable and refillable insulin pens.