How often do you change insulin on t:slim X2?

Today I transitioned to the t:slim X2 putting aside my dear Animas Vibe. I’ve always used the Inset-30 and will continue with the t:slim equivalent. Since I only use about 25 units of insulin per day, I’ve been in the habit of filing the cartridge with about 125-150 units and letting it run down before changing the cartridge. The minimum recommended fill for a t:slim cartridge is 120 units.

My trainer at the Joslin said that she would prefer that I change the cartridge every 3 days. Does anyone have experience stretching the cartridge to five days? I’d love to waste less insulin.

Thanks for your help!


Where did you get that idea? It’s actually 45-50 units (I’ve seen both listed), unless something changed. Unfortunately, there’s also 15-20 units dead space that it doesn’t count, so you would need a minimum fill volume of like 65 units, give or take.

It doesn’t hurt to try a lesser volume at the very least. I got the error message once that I didn’t have enough insulin in it (tried to re-prime a used cartridge after a software update). All I had to do was add a few more units to the cartridge and start the load process over again.

Personally, my needs are more than yours. I fill 200 units, which registers as “180+” (since you don’t get a specific number until after the first 10 units have been delivered), and change the cartridge every 3-4 days when the insulin runs out. I tried to do fewer cartridge changes, and do a maximum fill of 300 units every time, but found that process annoying. I didn’t like screwing new tubing onto old tubing, and always seemed to get air trapped in the connection. Or I’d have random spare tubing floating around in my supply kit. It’s much easier IMO to just change cartridge and infusion set at the same time. Given the occasional likelihood to knock an infusion set off, I already have an abundance of cartridges on the shelf. No need to further the imbalance.

Incidentally, I do suck the remaining 20 units or so out of the cartridge when I change, and add it to the next cartridge.

I routinely go 4-5 days before changing reservoirs. I’m using Humalog or 75/25 Fiasp Humalog. I’ve never had a problem. That might be different if you’re using something else.

I change my cartridge and infusion set asynchronously unless the stars align and both require replacement at the same time. I connect the tubing already on the reservoir to a new infusion set. When I change reservoirs I connect with the cartridge via new tubing. I go through infusion sets a lot faster than cartridges so I always have extra tubing ‘in stock’.

I generally get 6 days and sometimes 7 on a full fill up.

Thanks everyone. I think I’ll keep to my old pattern of changing my cartridges only when they are down below 10 units.

I use 30 units a day and I normally fill my cartridge with 250 units and let it run until it is empty. Never an issue in the last year.

On Novolog I could go longer, but on Fiasp I only get 3.5 days on the cartridge before I could start having issues.


When i started using tslim:x2 i asked if I could fill several cartridges and store them in the fridge to make the changes a little quicker. She said that i should not do that because the material used to make the plastic bag in the cartridge caused the insulin to degrade after 3 days.

Also, when on the Animas ping and now on the X2 the I have been told repeatedly that the infusion set should be used for no more than 3 days to avoid excess scar tissue at the sites. Note that medicare automatically sets the number of insets & cartridges at 30 for a 90 day supply.

Has anyone else been told this?

I haven’t heard that, haven’t experienced it and routinely use the cartridges for 4-5 days. I have doubts about the validity of that statement.

I’ve also been told that for many years and for much of that time I would go as long as I could with an infusion site, sometimes up to five days. After doing this for 30+ years I’m paying the price. Most of the area around my abdomen has some level of scar tissue. I recently starting using my thighs, and I’m changing sets every 2 days.

Well, that is at least one verified. I will try to check on the plastic bag next Endo appointment.

Here’s an article about insulin fibrillation that explains why we shouldn’t keep insulin in plastic, Including plastic reservoirs.

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This was true for earlier pumps as well. After 3 days insulin can start to degrade because it is in a plastic bag inside the cartridge. A lot of people leave it longer and it is ok. I do tend to notice higher bg if I wait too long so I change it every 3-4 days at most.

I am using more basal now so I fill it more, about 1.5 on the syringe. There is a huge problem still not fixed with the change cartridge load process, if you don’t have enough for 10 units through the tube you are in trouble. And there is no way to get out of the load process.

This happened to me again recently when I changed insets, I pressed the wrong fill button and then have to put 10 units through the tube. Once someone helped me when this happened with the cartridge, I used an old cartridge to trick it, but it didn’t work this time- I think I have forgotten what to do exactly.

I fill the t:slim with 300u and it lasts 5 or 6 days. I have refilled the cartridge twice to get 15-18 days per cartridge without noticing any problems. But a third refill (i.e. 4th use of the cartridge) gave me the sense that I wasn’t getting full doses of insulin: perhaps the little plunger-pump thing in the cartridge was wearing out.

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I use just under 30 units a day, so I don’t fill it. And yes, there are times when I get to day 3 and I still have insulin in the cartridge, so I let it go another day. I also hate wasting insulin, so I do run it dry which means sometimes it is in for 4 days.

if that happens again, you let the 10-unit fill start. Immediately after it starts filling you disengage the cartridge from the pump using whatever you use to remove cartridges. You don’t have to remove the cartridge, just disengage it. After the pumps says it has primed 10 units through the tubing, you press stop. Then snap back in the cartridge and you’re good to go.


My son used to routinely go 7-8 days between cartridge changes, and only changed then as a precautionary measure. But over the last couple of months, if we don’t change on day 6 the insulin goes bad. The transition from working perfectly to not working at all is a matter of about 5 hours. Last night my son was trending low at around 9pm so I cancelled his extended bolus. An hour later he started nudging back up, so I set a 250% temp rate. By midnight he was close to 10mmol/L (180) so I gave him a correction - it kept him level for the next half hour, then he started rising again. Gave another correction, did zip, nada. Sigh…cartridge change at 1am and another correction (ignoring the “IOB” which was doing nothing) finally got him back in range.

I go 5 to 5.5 days. I know the recommended interval is 3 days like the infusion set, but whats funny is Tandem knows we don’t abide by this. When I re-order, they ask if I need reservoirs with my order.

Thanks! :blush:

I just “upgraded” to the t:slim from a t:flex (that one holds 480 units of insulin). A full cartridge lasted me five and one-half days. I had no problems at all, except when using FIASP. With that, i found that I had to increase everything (basal rate and correction factor) by 25% after two days on both the t:flex and t:slim, and after three days, I got non-correctable occlusions 100% of the time.

Quite a few people (myself included) have some kind of issue using Fiasp on the X2. Lots o discussion about this. You might search.

I solved my problem with dilution Fiasp with Humalog (75/25). Then again, many people report no problems at all. Sure wish I knew the factors that contribute to success/failure but alas, I can’t find a common cause.