Are longer insulin needles faster to act?

We have discussed this several times in the past. I was convinced the longer needles were faster to act with insulin. To my surprise, I found out that, from this recent (Aug. 2016) super-large injection survey research paper, they are not:

Here is the Mayo Clinic review paper:

The report strongly recommends universal use of 4mm needles for pens (and 6mm for syringes):

“The shortest-length pen needle is 4 mm, but the shortest syringe needle today is 6 mm long (the syringe needle has to pass through the vial septum or stopper). Insulin pharmacokinetics/pharmacodynamics [i.e. speed of action] has been shown to be the same when injected into resting individuals using short and long needles.”

Presumably this assumes you’re injecting into subcutaneous tissue, rather than muscle or vein, right?

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The idea that shorter needles are better are based on a few simple concepts. a) Better patient compliance - shorter needles are less scary and may hurt less, so people with take their shots when they are supposed to. b) Less risk of IM injections (which are a perfectly reasonable thing to do for speed).

But the data they they used to say 4mm is equivalent to 8mm was cherry-picked to get that conclusion. If you look at the referenced studies, there are significant problems with them, and some of them even contradict the conclusion.

The first cross-reference:
“Maximum concentration and area under the curve for 0 to infinity min for insulin were bioequivalent for the 32G × 4 needle relative to the 32G × 6 and the 31G × 8 needles.”

But that :arrow_up: is not what we are talking about though, we are talking about speed.

“The time to the maximum insulin concentration was bioequivalent for the 32G × 4 needle relative to the 32G × 6 needle, but not the 31G × 8 needle.”

There is the statement :arrow_up:that the speed is not equivalent. That refutes the whole argument.

The second cross-reference:
The study was done on patients and their BG was monitored for 3 hours while they remained lying down?!

"The absorption rates were followed continuously for 3 h with the patient in the supine position. "

That’s pretty far from real-world. Use the 4mm when you are going to remain lying down for 3 hours after your injection…

The third cross-reference:
“Injections were administered at an approximately 90-degree angle into a raised skinfold for the 8-mm injection depth and without raising a skinfold for the 5-mm injection depth.”

Doing it for one and not the other is not the same thing. Raising the skin effectively removes the depth advantage of the 8mm needle.

As a side note, the 3rd study used 28 people, and did it twice. That’s a total of only 56 injections they are using for their conclusion. That’s less than a week of injections for me.

What I find very comical, but somewhat sad, is that all the people who are clamoring to get Fiasp could basically get the same speed improvement by simply taking their current rapid - NovoLog, Humalog, or Apidra - and just inject it IM. That would essentially be as fast as the Fiasp studies have shown.

Most of the professional diabetics inject IM.

Have you ever tried the 8mm needles? Why not try it.

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I have and didn’t really notice much difference but it was when I was new and didn’t have as much experience to properly judge, possibly. The majority of my ‘career’ I’ve used 6mm, and only recently switched to 4s, a transition in which I noted no difference… except for comfort-- although I firmly believe that the improved comfort was due to a superior needle design and not due to length… recently my insurance changed preferred needle brand. And although still using 4s, I find them less user friendly than the 6mm of my own preferred brand…

@Eric I’d be willing to swap a box of your favorite 8s for my favorite 4s and compare notes…

Ok, we can do that.

I think this stuff is hard to prove without a glyco-clamp, but if you were to test this sort of thing, I think a few factors for a better experiment would be:

  • Not doing a pinch with one set, and a non-pinch with the other. Do them all the same.
  • Doing it more than twice per test subject!
  • Have the subjects participate in normal life, not lie supine for 3 hours.
  • Do them with all types of injections, such as correction and bolus (basal doesn’t tell you anything about speed).
  • Just in general, doing a bigger sample of injections. Weeks or a month.

BTW, I have some 4mm needles already. But I can get a box of 100 for $13, shipped free with Amazon Prime. Which is probably cheaper than what it takes to ship to AK. :slight_smile:

I could send them for less than that… but the main point is comparing my favorite 4’s to your favorite 8s… length is length and needles aren’t hard to come by… I want to determine if my preference for shorter needles is psychological or if there might actually be a mechanical advantage or disadvantage… and I don’t much care what any of these studies say… real works n=1 observation will always be my gold standard… you’d be getting a box of novofine plus 4mm…

Ok. I don’t have a “favorite” in terms of quality. I used BD syringes for decades before pens came out, so I naturally gravitated to BD needles. But I have not compared different brands. But really the difference is primarily the length and quality. I don’t care about comfort. That’s never been a big deal. I just like quality stuff, not crappy needles where you have a bunch of bent ones or damaged or whatever. I think BD makes good stuff.

So I’d be sending you BD 8mms, 31 gauge.

But again, my observations are strictly for speed. Comfort means nothing. If you want comfort, get a different disease. :stuck_out_tongue:

@Eric @Sam There does seem to be something to this needle length thing.

I have never paid attention to the length of the needle I use. I just checked and the pen needles are 8mm and the syringe needles are 12.7mm.

I always change my penfill cartridge when there is less than 100 units left, and put the old cartridge in the fridge to use at home. I inject the almost used cartridge insulin with the 12.7mm syringe, and I do notice that I seem to get a slightly faster onset when I do this. I’ll have to pay more attention to this phenomenon in the future.

Concerning comfort, length does not seem to matter. I use the pain level of an injection to gauge when I should change the needle. If it hurts, then I change it.

Needle pain was the 14mm (?) 25 or 26ga needles we used to use. That sucked.

As an aside, I frequently ask my patients if they know what the greatest improvement in dentistry has been over the past forty years. After a couple of wrong guesses I tell them it has been in the hollow needle. The points are now laser sharpened, not mechanically sharpened. The metal encasing the cannula is thinner, resulting in the same size cannula being available in a thinner needle, and the lubricants used on the needles today are much more efficient than they used to be resulting in a lower friction more comfortable injection.


I like novofine better than BD… BD is what I use now because it’s what my prescription formulary switched to… BD are pretty good, but novofine are truly the Cadillac IMO… I’ve used both quite a lot. I’ve also used quite a few cheapos that I order on amazon just to experiment and build my stockpile… you do seem to get what you pay for…

You’ve got me thinking it might be a worthwhile experiment. I haven’t used 8s since newly diagnosed and much has changed since then… on the other hand the discussion about the speed differences between 4mm and 8mm needles is purely an abstract notion for me since I have afrezza which is 10x faster than either…

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I do think IM is pretty close to what Fiasp is reported to be.