Why Smaller Shots of Insulin Get Absorbed Faster, Peak Sooner, and Are Out of Your System Quicker


| Nov 28, 2007

For my contribution this month, I wanted to share an important lesson I learned about twenty years ago from Peggy Wong at the UCSF Diabetes Teaching Center. It concerns how long insulin lasts after you push down that plunger and create a "depot" of insulin under your skin.

We know a shot of insulin does not make a perfect sphere when injected, but it does create a pool of insulin in the subcutaneous tissue that approximates a ball or sphere. After the insulin is injected, it starts to be absorbed by the tissue it actually contacts. As you will see from the formulas and examples below, the larger the shot, the more time it takes to be absorbed by your body.

In the chart below, we have calculated the volume and surface area for seven different-sized injections. You might remember from a past math class that the radius of a sphere is the distance from the center to the surface of the sphere. The chart shows that as the radius (r) grows, the amount of surface area in relation to the volume gets smaller and smaller.

For example, let's say you test your blood sugar and it is 220 mg/dl. You decide that you need 4 units of insulin to bring it back to 100 mg/dl.

Let's look at the chart to see the difference between taking one shot of 4 units versus taking four shots of 1 unit. Both provide equal amounts of insulin.

With the 4-unit shot, there is only approximately 0.6 mm of surface area available for the insulin to "escape" into the surrounding tissues. With four shots of 1 unit each, there is actually 0.96 mm of surface area - about fifty percent more!

So which one do you think is going to hit the blood faster? Yes, the one with the most surface area. In fact, I have had healthcare pros recommend splitting up a dose like this to get a high blood sugar down. And one of the syringe makers once explored the possibility of making a "sprinkler" syringe, in which the insulin would come out of holes up and down the shaft of the needle, creating many small depots and, therefore, faster absorption.

Volume = 4/3 πr3
Surface = 4πr2

units of insulin* surface area
in mm squared
1 0.24
2 0.38
4 0.60
8 0.95
16 1.52
32 2.41
64 3.82
*1 unit of insulin is .01 ml

Looking at the chart, you can see that as the shot gets larger, there is less and less surface area as compared to the volume of the shot. This forces the insulin to wait longer to be absorbed, because the insulin molecules in the middle of the injected ball won't come into contact with the tissue until the insulin molecules surrounding them get absorbed first.

Another problem with large shots is variability in absorption. The larger the injected ball of insulin, the longer it will be there, and, therefore, the more unpredictable it becomes. Absorption is affected by body movement, which can hasten absorption, and by changing temperatures, both within the body and in the environment outside the body. Hot tubs, for instance, speed up absorption. If you get into a hot tub after taking a large shot, more insulin is mobilized by the heat than would be after a small shot.

I feel that all insulin users should try to understand as much as they can about this powerful, wonderful, lifesaving drug. So it is crucial to understand the mechanics of how insulin is absorbed. I hope that this little math lesson helps.

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Posted by dorisjdickson on 29 November 2007

Thank you!

As a 31 year veteran, I try to teach naysayer diabetics this technique - to take smaller amounts of insuln at a time. Some listen but many give me "what proof do you have." Maybe this will help!

Posted by Anonymous on 29 November 2007

Yes Yes Yes...I am on the pump and I KNOW that "broken up" doses help tremendously. Just yesterday at lunch I took a small dose, waited about five minutes took a littler larger blous, then "finished off" my mealtime bolus with yet another small bolus at the end of my meal. I have found that particularily with a fat laden meal (such as I had at lunch yesterday) that this method helps a lot. But even for "regular" boluses..this always help me to get my insulin to "work better"..but Scott is right, do what works best for you and if this just one of many "tools" to deploy, then go for it. Any good result is worth the extra "effort" involved.

Posted by Anonymous on 29 November 2007

This is good information and if you are on the pump it can be done easily but if you inject with a needle device you become a pin cushion. I do like the idea of a sprinkler needle. Any one thinking of coming out with such a device?....Jim

Posted by Florian on 29 November 2007

Scott,great article. As a retired BioScientist and a practicing Type 1 with 40 years of experience(20+ on MDI),I always injected small amounts of insulin believing that it was a better way to increase the absorption. I also injected the split doses of insulin in the left side and the right side of my body believing that the distribution of insulin through my entire body would be faster. My A1C test results were always in the 5 to 6% range.

Since last June I have been using a pump and I started splitting my meal insulin doses and bolusing before and after eating.
My first A1C after 4 months on the pump was 5.6%

Posted by Anonymous on 29 November 2007

This type of information is awesome. Its another trick to add the diabetes regimen. Something MacGyver might use if he had diabetes...love it. Diabetes is a major pain but the more things I learn the easier it is to treat, sort of a cat and mouse dynamic. Keep these articles coming.

Posted by Anonymous on 30 November 2007

is this the reason why Lantus is a 24 hour insulin?
if i will divide it to 2 shots will it be a 12 hour insulin but twice as effective?

Posted by Florian on 1 December 2007

When I was doing MDI using Levemir and Novolog, I split the Levemir dose 1/2 in AM and 1/2 in PM in addition to using small multiple doses of Novolg for meals and corrections. It was experimentation and trial and error that got me to where I had good control for a "manual Pancreas."

Posted by Anonymous on 1 December 2007

Lantus does not last 24 hours in me, but can in others. I divide my dose in half, and take it twice a day instead of once—about every 12 hours. It's true that this smaller does won't last as long as the larger, but it is not as dramatic as what anonymous above asks. Each smaller shot shot lasts maybe 18 hours, so there is plenty of overlap, so I am never "out" of basil insulin.

Posted by Anonymous on 2 December 2007

Thanks, this is a really interesting article.

Posted by mjensentulsa on 7 December 2007

Scott -

I'd be interested in how this works in an infusion (i.e. pump) scenario. My Medtronic lets me take a bolus "immediately" or over a period of time, in 30 minute increments. The former is like "pushing the plunger," but the latter seems too long to wait if I am having a high. Do you know if pump manufacturers have studied this issue, i.e. in terms of timing those immediate boluses for optimum absorption? Seems like a five-minute duration for a single dose might give more effective distribution than a "plunger bubble."

Posted by Anonymous on 28 December 2007

what i have done with high blood sugars is give myself a shot in my muscle and then try to work that muscle to get the insulin to absorb faster. For example, the other day my sugar was at 300, and 1u of Humalog lowers me about 125 pts, so i took a 1.5u into my arm muscle, and while i was driving to a customer on the highway, i exercised my arm and my sugar was down to 150 in about 30 minutes...

Posted by Anonymous on 31 May 2008

Another worthwhile coverage might be the fact that U-100 is significantly slower than U-40 insulin was, and in fact, U-40 was about the same speed as today's analogues are ... making one wonder whether today's "advances" are really just a scam to bilk today's consumers out of our money!

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