Fiasp with Tandem t:slim X2

About a month ago, I switched from Novolog to Fiasp for my t:slim x2 Pump. Since then, I’ve received so many new occlusion alarms. Called Tandem & they said Fiasp was not supported for their pumps yet. The rep indicated that multiple people have called about this problem. Usually the occlusion alarms start on the 2nd day of the last cartridge/infusion set change. And when I switch back to Novolog, the occlusions stop altogether. This brings up 2 questions for me: 1) Why would my endo prescribe this insulin without Tandem’s support. 2) Are others having these issues with Fiasp/Tandem t:slim X2?

I’m seriously thinking of dropping the pump all together and resuming MDA with Fiasp/Tresiba.

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I have been using Fiasp for a while with mine and LOVE IT!
That being said, I have had occlusion alarms all day today.
I rarely get these. But today is a real one.
I think today was because I had in set get caught on something and it probably tweaked the cannula.

I find that most of the time there are two types of alarms. One is because I didn’t get all the air out when I fill the cartridge. I did this a few times when I first got the X2.
Second thing, if the pump gets too hot, I think the Fiasp has issues.
If clearing the alarm and resuming insulin doesn’t solve it, try wearing it in a different location to see if the temperature might be the problem.
When filling my cartridge, I pull air out of it first, then put insulin in my syringe. Then when putting the syringe in the cartridge, I pull as much vacuum pressure as possible, tap it a number of times and wait until ALL the bubbles rise to the top before pushing the insulin into the cartridge.
Take a few seconds longer, but works like a charm!

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I use Fiasp (so far three months) in my Medtronic 670G and I have yet to experience any occlusion issues.


Docs are allowed to prescribe off-label.

No. Works great for us.
We do not get occlusions.

Same. Except you described it much quicker. It would have taken me a small novel. Nice concise write-up !!!



The one thing I find surprising regarding your conversation with Tandem Support was their use of the word “yet” which has obvious implications.

So, just double checking if they actually said “yet” or if that was just the way you happened to write the post?

I don’t remember which thread it was mentioned on but someone posted that switching to steel sets completely resolved the occlusion issue with fiasp and the X2.

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She didn’t actually say “yet”. She simply stated Fiasp “wasn’t supported at this time”.

Great suggestion Hammer. I’ll give it a try, as I have to change my cartridge today.


Got it.

Would have been more interesting but reality is better than something which is not.

I do believe that Novo Nordisk is applying for approvals for both Pediatrics and Pump Usage for Fiasp but the part I have no idea is if the Pump approvals will be for all pumps currently approved for Novolog (as it is almost the same thing save for two additional ingredients) or if the approval would be for very specific pumps.

We will see…

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I also do the same. You can easily pull 3ml of air out of the cartridge before injecting insulin into it. Also make sure you hold the the pump sideways with the tube on the top while filling the tubing.

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Oh yeah, one other thing.
The X2 pump will get pretty warm if you charge it up from a low battery charge.
If you keep it topped off, and don’t let it run all the way down, the charging doesn’t warm the pump up nearly as much.
I feel this extra heat is something that causes issues with insulin in general, but Fiasp is a little more sensitive.


I’m glad that I found this thread. I don’t need to start a new one. :slightly_smiling_face: I just started using Fiasp earlier this year (and, honestly, I thought it was pretty new and didn’t realize it’s been out for almost two-years…where have I been?)

Anyway, I started wearing my X2 again in June of this year after taking an extended MDI break. I rarely got any occlusion alarms. A few days ago I started getting them all the time. I called Tandem support and they walked me through the troubleshooting. They replaced sets, but the occlusions kept happening. As an FYI, I’d had occlusion alarms daily using both the TruSteel and AutoSoft 90 sets.

I called last night and a rep finally asked me what insulin I was using. He then let me know that Fiasp isn’t supported for the X2. :broken_heart:

I removed my pump as it’s just been a frustrating few days and I’ve pretty much been injecting insulin anyway to make sure my blood sugar wasn’t going too high, so I’m back on MDI.

If it’s been over two years, I don’t know if I have much hope that this is something Tandem is fast-tracking. I was looking forward to starting the closed-loop system on the X2 soon too because I’m on my last G5 transmitter.

I’m sad, but I’ll start exploring the progress of the closed-loop that Omnipod is working on. :cry: I searched and Fiasp is approved with their system.

Thanks for reviving this thread, @Regina. I’m coming up on eligibility for a new pump in March and have been considering switching to Tandem from Medtronic. I use Fiasp with my current pump (an old-school pager-style Paradigm) and it’s never been a problem. But I hate occlusion alarms above all things, due to a bad experience with a different pump several years back (the short-lived Assante Snap). Just about drove me to tears. So your story is cautionary for me. Ugh. I wonder if anyone with more recent Tandem/Fiasp experience wants to weigh in.

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FWIW, here’s the official word from the Tandem site:

Tandem pumps and cartridges are only indicated for use with Novolog and Humalog U-100 insulins. Importantly, clinical studies using our automated insulin delivery algorithms were only conducted using Humalog and Novolog U-100 insulins, which have different times of onset compared to Fiasp.

If you use Fiasp in your pump and you begin experiencing persistent issues that can be attributed to insulin compatibility, we can’t guarantee your warranty will be honored.

Do you have plans to expand your pumps’ Indications for Use to include Fiasp?

We do not have immediate plans to seek approval for use of Fiasp in our pumps.

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@Regina Ask your doctor to switch you to Lyumjev instead. Terrible name, but it’s supposed to be really fast acting and have better success in the T:slim.

Unfortunately, FIASP tends to crystalize under the pressure the T:slim puts on it. Medtronic and other syringe-piston type pumps are essentially an open line. You push the back end, insulin comes out the other side. Tandem though has two isolated chambers, as a patented safety mechanism. It keeps you separated from all the insulin you’re carrying. But since it’s a more sealed system, FIASP doesn’t respond nicely to the increased pressure placed on it.

Lyumjev is the newest insulin on the market, so it is not yet appproved for use in the T:slim either. But many have reported no occlusions like they had with FIASP. You should use the site search function for Lyumjev, and you’ll find the reports of several Tandem users. Note: site irritation does seem common to both FIASP and Lyumjev.


This is great news. Thanks, @Robyn_H!

Because I was on MDI an extended amount of time before putting my pump back on, AND I literally just picked up Fiasp from the pharmacy, guess who is going to be on shots for the next few weeks? Me.

However, I have an appointment with my endo next Tuesday, and I’ll request that prescribe Lyumjev for me. Then I can try it once I exhaust my Fiasp supply.

I know about irritation with Fiasp. I’ve been lucky and haven’t experienced that. I’ll do a little research into Lyumjev, but it pretty much feels like it’s a no-brainer for me. Plus, my insurance tends to like insulin made by Lilly, so I’d already considered switching because of that. Now I don’t have a choice.

Thanks for this!!!

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No problem.

Just a few notes, though… Go into your appointment forewarned, Apidra is another option similar to FIASP, but it is not Lyumjev. I don’t know where you are, so Lyumjev might not be approved yet there, and/or your insurance company might make you jump through a few hoops to get it. If you can’t get Lyumjev yet, and your Endo suggests Apidra, it also had mixed results in the T:slim. Seems to be 50/50, with half the users reporting occlusions and the other half having no problem. I wouldn’t buy more than 1 bottle of Apidra until you see how it works out for you.

I can’t remember who, but another member here reported solving the occlusion problem by mixing either their Apidra or FIASP with Humalog or Novolog, half and half. They still saw faster acting insulin than Novolog/Humalog alone, and no longer had the occlusion problem. If you have any Humalog or Novolog left, maybe give mixing them a try in your pump?

Last note: if you’re using Control-IQ on your t:slim, you can’t change the duration of insulin action to better align with Lyumjev. (The difference is much more marginal with FIASP and Apidra, so doesn’t matter much here). The Control-IQ program was written for Humalog or Novolog. I suspect they’re going to unlock this setting in the next software upgrade, but until then… You will probably notice the pump reports a little more insulin on board than is realistic, since Lyumjev has a shorter tail. It’s not a significant problem, but the pump might suspend your basal unnecessarily. That can be addressed by raising your correction factor SLIGHTLY, though.

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When I was using a t:flex pump, if I loaded up the full 480U of Fiasp, I got occlusions every time.

Until today, I haven’t had that happen with my t:slim x2. I used Fiasp for the first time in maybe six months. I used to get 3 cartridge fills from a vial then throw out the remaining ~60 or so units. Then I decided to try what some people here had suggested: top off the cartridge with the last bit of the vial. That worked find with Humalog, Novolog, and Lyumjev.

Yesterday morning, I topped off the cartridge with the last of the Fiasp vial. No problems yesterday. This morning, my BG was 172 (using Control-IQ, it is typically around 118). And it promptly went steadily up to 248. So I knew what was happening. Sure enough, at the end of a correction bolus, I get the occlusion alarm. So I got an extra day out of the cartridge. But when I changed my setup, I used Lyumjev.

What I had forgotten in doing the topping-off was that what works OK with Fiasp is to just use the last of a vial in a new cartridge/infusion set and use a new vial to make up the difference to fill the cartridge to 300U. My bad!

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I got a new job, so I got new insurance. Guess whose insurance company covers Lyumjev? Mine.

I’ve been using Lyumjev for a couple of sets. The only thing that’s interesting is Lyumjev sometimes burns going in. I can feel it when I give myself a bolus. I know the same thing could happen with Fiasp, but I never experienced it. It works to control my sugars and seems to work in my Tandem pump well, so I’ll put up with it.

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I’ve been using Lyumjev a lot recently. I do a combination of multiple daily injections (including Lantus) and Afrezza. I haven’t had any pain at my Lyumjev injection sites, but I do seem to get more bruises than I did with Humalog.

I’ve been interested in potentially transitioning to a tandem pump and using Lyumjev because Lyumjev has such a quick action time. I’m hoping Tandem’s most recent update will allow for targeting 90-100 mg/dl at night, rather than 110.

Anyway, I’m really impressed! I mean honestly, Lyumjev is more consistent than Afrezza and works almost as quickly. I know some people have said otherwise, but that is my experience. Afrezza seems to be better at levelling me off around 70-80 as long as I took a reasonable dose whereas I have to be more precise with Lyumjev - the risk of dropping low is higher.

That seems like that might work alright with a Tandem pump with Control IQ though.

Anyway, just thought I’d share my experience. I’m generally using it more than Afrezza now and just using Afrezza when my dosing with Lyumjev is off. It has been working pretty well for me so far. Fingers crossed that Tandem provides more target options for Control IQ in the next year or two.

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