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

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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  1. 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.

  2. 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

  3. 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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