Fiasp: How long can it stay in your pump before going bad?

I have been using Fiasp a little while now, and it works well for the most part, but I have started to notice a trend when my boluses just seem to stop working after a few days. At first I thought it was just bad pump sites since that is a CONSTANT issue for me, or has been, but seeing as it seemed to happen after a new site was put in, and inspections of the new site didn’t have the same characteristics of what I usually experience, which is leaking, or pooling up of insulin under the skin that never absorbs. One time recently I had just put a site in and my BG wouldn’t come down, so I thought it was in a bad spot, it looked fine after taking it off, and I put a new one in. BG still wasn’t coming down, so I got to thinking maybe it was due to the insulin in the cartridge going bad. Swapped the cartridge and then BG started going down. I have since noticed a pattern where things just don’t seem to be working at all after about 2.5 - 3 days after changing the cartridge. Has anyone else noticed this problem?

I tried using fiasp a few months ago. Each time I used it, it worked for a day and a half to two days, then stopped. By day three my blood sugars were going high, so I stopped. At least with my novolog, I can go as long as four days without changing my site, although ideally, I change them every 2 1/2 days as I have extraordinary sensitive skin.

As a side comment: When I insert a sensor, I use skin tac, which has worked great for years. When I went to get blood taken this past week the phlebotomist used “regular” medical tape. Taking it off later that night I had two big welts from the tape site.

I’ve been using Fiasp in my pump for two years. I’d guess that a cartridge lasts me anywhere from two to four days, and I haven’t noticed a problem. I do use metal sites and I do change sites daily, because I have problems with reacting to the cannula and the tape. Fiasp does seem to contribute to infusion site irritation. I change my sites at the first signs of itching or pain, which often happens within 12 hours of insertion (but since I use metal sets, they’re easy to remove and put in a new location and re-tape).

I had the same problem. There are several posts on this subject with good info. I’d recommend looking at them.

I was able to resolve the issue by using an 80/20 mix of Fiasp and Humalog. That’s worked well for several months.

We have been using Fiasp in our X2 since last Summer.
We do not intend to ever go past three days with an infusion site. And our Endo has very specifically told us never to keep the infusion site in past 3 days max.
We forget sometimes.
And yeah - we generally have bad BG problems at that point.

Which is quickly resolved by a syringe followed up with a site change.

On the other hand, this is the same behaviour we noticed with Novolog and Humalog. So although we appear to get very bad absorption after 3 days, it is not different then the other two insulins we have used.


I’ve pumped FiASP for the past 3 months and generally use no more than 25U over 24 hours (enough for 8 days reservoir supply).

I change sites every 3rd (ok, sometimes 4th) day but continue to use same reservoir and line previously loaded with FiASP. I’ve had no noticeable loss of efficacy. I also keep my Animas pump in my pocket against my body (heat) as the clip broke off a couple of years ago.

New infusion sites often don’t absorb insulin normally for several hours after initially started (local trauma at the site location).

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I should clarify that I almost always change sites every 2 days or shorter, as they don’t last any longer than that for me. I inserted a new site last night, no leaks, everything working fine, BG started rising sometime in the night and when i woke up it was close to 280-300 (I had very little carbs that night). So this morning I have continued to correct for several hours and have probably taken about 20 units, and things have only barely budged with nothing but a tiny amount of carbs. The cartridge I am on is close to 3 days old now. There don’t appear to be any issues with the site, so I am leaning towards the insulin being the issue. I may head home and swap my cartridge but leave the site and see what happens as an experiment.

For us, a new pump infusion site works immediately. It is old sites (over 3 days) that do not work well for us.

But a syringe (for us) always has faster onset of action as compared to pump bolus via an infusion set site. So for a high BG, often times a syringe is the more effective way to treat, for us.

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I found the depth of the cannula to make the biggest difference for me. The angled ones would be bad in 2-3 days. 6mm 90 degrees, same thing. 9mm 90 degrees, I get 3-4 days with very few issues.


I’ve been using Fiasp in my Pump for about six months. My reservoir/infusion sets last 3 to 4 days. Rarely experience any issues regarding insulin effectiveness.

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I think part of what may be going on is related to the fact that some people find Fiasp “stings” a bit. Irritation means inflammation means impaired absorption. But not everyone experiences that, so as always YDMV. For my part I have felt it from time to time, especially in my first few months on it, and more redness/sensitivity at the canula site after removing an infusion set, but mostly I don’t. I’ve also noticed more of a 3rd-day fade than with Novolog or Humalog, but for me the advantages outweigh the disadvantages. In any case, if changing sites without changing the reservoir eliminates the issue or precludes it as you describe, that suggests the problem can be more with the site than the insulin itself. I have noticed that Fiasp seems thicker or more viscous than the standard analogs, which may cause it to build up around the canula rather than diffusing further out into the dermis, which could also be a problem.


Hmm I was coming here to see what kind of issues, if any, that people were having with Fiasp. I need something that acts a bit faster and better for me than Humalog right now but if what you’re saying is correct re: fiasp being a bit thicker & a lot of other people are having some issues with it, I bet it won’t work for me. I’m guessing it seems thicker because of the B3 in it?
Super frustrated lately trying to figure out whether its the actual insulin itself that my body has built up a tolerance to or if I jusy continuously need to increase my rates of everything.

I wouldn’t decide that based on a few posts here. Mostly I think it’s terrific. I was having a really hard time prebolusing for meals on Novolog—it seemed to be getting slower and slower for me, to the point where I was doing it an hour out from mealtime, especially if I was experiencing any work stress, which exerts an upward pressure on my BG. With Fiasp, 15-20 min is fine. And I’ve only noticed the sting thing intermittently early on, not a big deal–I haven’t had it at all for a long time.

My endo got me a single vial to try out before I changed my scrip to it. You might see if you can do that. Definitely worth a try.


I agree with @DrBB. You’ll never know how FiASP works for you until you try it. My endo had told me it was no different than Humalog - he obviously was completely biased by 1 or 2 patients.

I was on Humalog for 23 years and its onset was often > 60 minutes or more, forcing me to pre-bolus long before in ate. FiASP onset for me is consistently less than 15 minutes.

It’s a keeper for me

I am using FIASP exclusively now in my Tandem t:flex. BUT…I can only fill my cartridge/reservoir with ~330 units, which is 3.5 days use for me. After that, I get an occlusion 100% of the time. With Novolog, I can fill the cartridge all the way to 480 units and get 5 days’ use.

With respect to to how I like FIASP, it is about the same as Novolog, a little faster on starting my BG downward. And I use about 85% as much as with Novolog. But my duration is the same - 3:45 hours.

Mine said that it was the same thing as Apidra and wouldn’t give me a script to even try it, which is one reason I am going to go to a new endo (he also refuses to do lab tests I ask for claiming that anything other than what he orders is essentially meaningless).

I am still on the fence with FIAsp. I will say I have been trying to use flexible cannula sets for the past couple weeks and I think that, just like Humalog, they simply don’t work well for me. I think I was getting better results with the stainless steel ones, but they are pretty uncomfortable for me. Even with those I was starting to have some degraded performance. I am kinda at a loss here as I can’t get any consistency with anything these days.

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my Endo gave me a sample vial of Fiasp 6 months ago and it worked well for me, so I’ve stuck with it. It does seem to bring highs down faster so I no longer overload (and go low, often) trying to correct them. Haven’t noticed any other differences myself.

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I just got ahold of a couple sample vials of fiasp from my endo yesterday! About to try it in a new pod!


Post your experience with the Fiasp.

So far so good! It actually works, as opposed to Humalog for me. I can kinda feel it a bit more when it goes in, so I understand why people say it burns.

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