The Newest Fast-Acting Insulins – How Fast Is Fast?

I think it’s time for me to send out an update on the new ultra-rapid acting insulins, but before I jump into what’s new, let me back up a minute and talk about what’s “old”.

Most of us use a rapid-acting insulin of some kind- mostly either Humalog or NovoLog.  But we all know that these insulins are a FAR cry from rapid acting.  In fact, they are quite the opposite.  How many times have you been high, taken a dose of “rapid” acting insulin, then looked at your CGM 30 minutes later (or tested) and your blood sugar hadn’t moved at all- or even gone UP.  WTF?!  Super frustrating and the number one cause of rage boluses in my personal situation.  Oh, 5 units didn’t budge me at all?  Nothing a 10 unit rage bolus can’t handle.  Annnnnnnndddd now I’m grumpily eating crackers with an apple juice chaser.  And peanut butter for some reason….

Unfortunately the myth of rapid-acting insulin perpetuates our mentality- for both people with diabetes and physicians, that we still think we can take the insulin and eat right away.  This might work if you have significant gastroparesis, but otherwise, you will be WAY behind the eight ball.  That’s one reason Steve and I always push the “pre-bolus” or bolusing a minimum 20-30 minutes before you eat, and longer if the glucose level is really high and/or with trend arrows shooting upward.  This was actually one of my most vivid memories when I was first diagnosed and in the hospital.  They brought me my food and gave me my insulin but made me sit there staring at my food for 20 minutes before they would let me eat!  Nothing like not being able to eat to let a 15 year old kid know that his whole life just got F’d up.

So can these new “ultra-rapid acting insulins” get us away from the pre-bolus and enable us to take insulin when we actually eat?  I’m sorry to say, but I just don’t think so.  Not yet.  I should clarify that I’m NOT talking about Afrezza which you actually CAN (and should) take when you start eating… or even after eating because it is that fast.  I’m talking specifically about the new “faster-acting aspart” or Fiasp.  This is basically the new NovoLog that just hit the shelves about a month or so ago now, and you may start hearing about.  Basically it adds a couple of excipients to the NovoLog we all know and love to make it get absorbed a little bit faster.  So how fast is faster?  Well, a little, but not a ton.  In the first of the clinical trials, Fiasp lowered A1c by about 0.1% compared to regular NovoLog with some small improvements in BGs after a meal.  So not a huge difference, but a difference.

My take on it is really this-

  1. Some people seem to notice a difference when switching, but I personally didn’t, nor did Steve.
  2. If you are going to switch, I would just go into it with low expectations so you aren’t all devastated if you don’t like it.  This is my approach to movies as well and it works well for me.  Was still disappointed by Pitch Perfect 3 though.
  3. Also, and most importantly, I personally would STILL pre-bolus before eating.  Fiasp is a little bit faster, but not enough to make me really believe you can avoid pre-bolusing.  Don’t worry, it’s not super-dooper fast to the point it will make you crash, so you definitely still can give it a run up before eating.  Having a CGM will help you figure it out.
  4. It’s supposed to be priced the same as NovoLog, so you might just adopt a “why not” approach to trying it.
  5. Even though number 4 is true, it still might be a hassle to get for these early days since it’s new.
  6. You will probably have to remind your provider that it exists and you want to try it.  Then sit back and enjoy the moment where they realize you know more than them.
  7. It MIGHT have the best benefit in automated insulin systems like the 670g or for you LOOPers out there since it can take care of the basal for you and really highlight any mealtime benefits.

Ultimately I think having a truly fast-acting insulin that you can inject or put into a pump is the single biggest need for insulin therapy in T1D. So for that reason, I’m super super glad to see companies working on this.  Out of the gate with Fiasp, I don’t think we are “there” yet, but I hope it will continue to push insulin therapy in this direction.  With that in mind, numerous other companies are working on their new, faster-acting insulins, so we will have to see just how fast their fast is.


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    A big issue especially for retirees on Medicare Part D is not only getting Fiasp approved (because it will not be on any formulary), but getting it down from Tier 3 or 4 to Tier 1 where Novolog is. Until then, it’s try it then forget about it because of Part D cost.

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      As I approach 65 and my concern of the price of insulin I decided to take a trip to Canada As you well know Novolog is 300 a vial. I crossed the boarder and boght NovoRapid/ Same thing as Novolog and paid 26 a vial US. I will be more than happy to make a trip up north to buy supplies. And boarder patrol is well aware of what is going on.

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        How far are you ftom Canadian border?
        Any possibility of a Buyers Club under your wing?

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        Glen, you may not be aware that Medicare will pay for your insulin (not part D) under part B if it is used in a pump, there is no copay.

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        @Tom Loss What happens now that the border is closed? Can you claim that the trip is a matter of medical necessity? Have you dual citizenship so the Canadians have to let you in and the Americans have to let you back. Here, we have a 14 day quarantine in effect, if you leave Canada and return or just enter the country, but I gather that is not the case in the U.S.

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    I have been using Fiasp since it became available in Canada. I find that it works well for me. If I prebolus, I go low before I get to eat my food. And for some foods, I need to bolus after I eat. When I was pumping, I could do an extended bolus but on MDI I find it works better this way. I use CGM to help me see how foods react

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    I just tried FIASP in my TandemX2. I don’t notice a difference even when using it for correction. I haven’t tried pre blousing yet. That is the next step. Maybe ten minutes before. Thanks for the review. Very helpful. I have always taken my Bolus when I am ready to eat and sometimes after.

  4. Hi Jeremy,

    Thanks for this very interesting article. It was forwarded to me by a great friend. We are working on several super ultra-rapid insulins at Protomer Technologies ( that have the potential to really change this field. We have engineered our new ultra-rapid insulin (the insulin itself) to be much more rapid, it is still in research and development but your article is well received given that we also think making super ultra-rapid insulins is a top priority in T1D and will have a big immediate impact.
    Best regards,

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    I am curious as to why you are not talking about Afrezza. It is proven to be faster than Fiasp and easier to use.
    Could you please explain why you are not promoting Afrezza.
    I heard Dr. Edelman say in a presentation that he is in fact using Afrezza himself.
    To me, that speaks volumes about the efficacy of Afrezza.
    Thank you in advance for your response.

  6. Never knew there was a newer injectable fast acting insulin. I’ve tried Afrezza, works great, but… I’ve had some terrible issues with coughing. Not just at time of inhalation, but continuously. Especially first thing in the morning. So much so, that I pulled muscles that are still hurting WEEKS/MONTHS after stopping use. Can’t wait to try Flasp. Fingers crossed….

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      Hope it works better for you Tabbie!

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      Afreeza not available in lower doses like 2 or 3 units. Too many lows on their lowest available dosage of 4 units. Don’t know why the company won’t make lower dosages for everyone who can’t handle 4 units for every sinfle blood sugar.

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    Afreeza dosing is off and only comes in 4, 8 or 12 unit packs. Not good. Some people don’t need 4 units. Afreeza doesn’t offer lower doses like 2 or 3 units. Too many lows using their “Lowest” dosage of 4 units. I asked the company to consider making lower dose packs but for whatever reason no luck. Just be careful with this insulin. Better have carbs, juice ready when the crash starts up. Very dissappointed in their response to make lower doses available for people who cpuld use it. I have even heard of people breaking up the 4 units packs into 2 unit packs which is dangerous.

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    I use the apidra and it is very fast i always use it 1-2 minuets before i start to eat and for some foods like sweets it’s just like i didn’t take my dose at all, at the end of the day i think that it depends on the Person

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      I’m still on apidra but it has never worked that fast for me. I’m still having to bolus 15 minutes before I eat or if I’m higher and 150 I still need to bolus 30 minutes earlier. What I’m wondering is this insulin faster than apidra?

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        Hi Jennifer,
        Fast-acting Apridra is not as fast as apart, and bolusing at least 20 minutes before eating is a good strategy with any subcutaneously injected insulin. With Afrezza, you may want to check your technique and possibly use a higher dose.

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        It’s faster for us. My dh was on apidra for years. I tried Fiasp and I had to be careful that I didn’t correction bolus or meal bolus too early or he would go low. Now, I’m very good at getting the right amount of insulin in at the right time with Fiasp. You learn to adjust very quickly and the cgms helps a lot as well.

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    Does anyone else manage their diabetes just with rapid acting insulin.? I stopped long acting and basal insulin 6 months ago and only use rapid acting insulin with meals now and lost 15 pounds and my blood sugars are still controllable. Just curious if anybody else has tried this ?

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      That is really Interesting Lena
      I would be interested to know more
      If you dose your fast acting correctly surely you don’t need slow acting too
      Also i am guessing you lost the weight due to your body not craving food in-between meals??

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      I was always told the body needs about 4U of fast acting every few hours without long acting.

      It is possible, and is done by people with pumps.

      I just personally wouldn’t do it where I’m a pen user.

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      Yes, I have used only humalog for 30 +years now.

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    I am so thankful for this review. I’ve been on the pump and on FIASP for about 6 months. Inexplicably, no one told me that I’d be “chasing” highs and then, exactly as you said, find myself shoveling crackers and juice at 3am. It also seems like if you dont catch it pre-bolus, its much harder to get it down after meals. So i will now try pre-bolusing at about 1/2hour before meals. Hopefully we’ll hear of newer and faster insulin soon.

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      Something I was told by a fellow t1d was that I had to change the setting on my pump from 4 hours to two or three hours for the active time of the insulin. I changed mine to 3 and I didn’t notice a difference either way. But for some of us insulin just doesn’t stay around as long as others

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    Just recently switched insulins from Humalog to Fiasp and I’m finding that my sugars rise after I’ve eaten my meal, although I did Experienced severe low after my last night’s supper about 1 hour after eating. Has this happened to anyone else?

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    My wife was outside in the sun for 2 hours at the Special Olympics, we didn’t have her pen with her. Her numbers jumped up almost 300 points in 2 hours from around 150 before we left to 440 when we got home. I probably should have scanned her sensor with my phone but she was constantly talking to different people. The rate of increase was really insane. She’s on humalog during the day and Lantus at night. She is on MA, so I doubt either of the two fast actings mentioned would be covered. We have a serious issue even keeping her in range.

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      Lantus works over 24 hours so you are on it for the entire day. Humalog is used for corrections and for meals and is gone in what? 3.5 hours?

      • Lantus is supposed to last 24 hours but its duration of activity will vary from person to person. Yes, Humalog is for correcting and for meals. Hope you can attend our virtual conference on Saturday as I will be giving a lecture on using insulin and the different options.

  13. I’ve been a T1D for 65 yrs and still don’t have a handle on control. currentle basal in the A.M. with Tresiba and i bolus with Apidra. I try pre meal 30-60 minutes prior to eating but nothing can keep up with the speed in which my BS rises. I’m always hopeful for a better product but also a realist.

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    As a 35 year T1D I was hopeful that the Humalog was going to be helpful over the Regular I was using prior. I’d always thought that Humalog was supposed to kick in a lot faster than it does for me. I’ve had post meal spikes that were reaching 300 after taking a bolus of 6 to 8 units for relatively low carb meals. Of course I’d bolus another 4 units to try and get my BG to trend down. I would see rapid drops occur 2 to 3 hours later where I would then have to put the brakes on with sugars. Not fast and sometimes hours later after a shot. Now researching injection site prefferences for better response.

    • You’re experiencing what every person with type 1 experiences taking Humalog. Try to take it at least 20 min before eating – that can help with the rise. Also consider taking Afrezza.

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    I think the best results from Humalog or Novolog comes from not taking in too much carbs and hoping the insulin handles it. I personally am type 2 and let’s face it. Most type 2 people are basically insulin resistant and that goes for human made insulin. It’s not like Humalog or Novolog would work any better if your own insulin doesn’t work well. I would say from experience using Basaglar for a long acting and Novolog for meal time that overall fasting levels improve but that’s about it. I see generally some similar spikes in BGL after a meal with Novolog as I did without.
    The only improvement was overnight I tended to be lower and slightly improve my average BGL. I would caution with Novolog not to take more if your numbers are not going down. You may end up overnight experiencing a low and see actually higher numbers from a dawn affect. I generally feel insulin as a treatment in general is both a positive and a negative. The side effects of potential weight gain, which only decreases insulin sensitivity is sort of working against the insulin.

    • Thank you, Doctor! Your experiences make perfect sense to me, and many other type 2s on insulin can probably relate.

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