I seem to recall having heard or read somewhere that it is not good to give an insulin injection of more than 7 units.
Does anyone know the reason?
I believe Dr. Bernstein suggests that more than 7 units in one location can lead to poor absorption. That just means that if you’re giving more than 7 units, you might consider giving multiple injections in different locations.
Does this mean that if one were to take 10 units for either basal or a bolus, to split the 10 unit injection into a 5, 5 at different location? wow…more injections. more body parts needed. Unfortunately, the absorption is different for different injection sites. That could affect BG. Darn.
Unfortunately, I have no practical experience because I’m on a pump and when I was on MDI, I never had to inject more than 7 units at a time. Maybe some Bernstein followers will jump in with some useful advice.
Well, what was said above is pretty much what there is to say. Bernstein says that a single injection of more than 7 units often leads to erratic or unpredictable absorption behavior, thus he recommends that larger injections be broken down into multiple smaller ones. That’s what I do if, for instance, we go out for pizza and I know it’s going to take 12 or 14 units–I do two smaller ones in two different sites a few inches apart that add up to the needed amount,
Thanks! That’s good to know. And I did not know about pizza requiring 12 or 14 units for you- wow. Do you bolus for pizza at the beginning of the meal, or do you spread it over time? Some people take part of the injection in the beginning, and then wait until later. Just curious what works for you and maybe your reasons. ( I realize that everyone’s diabetes is different.)
Thank you!
LOL. It takes that many units because I only eat pizza once every third or fourth blue moon, so on the rare occasions when I do treat myself, I don’t limit it to a slice or two 
I normally prebolus about the time the order goes in, so the insulin will start working about when the pizza arrives. Then I check about 90 minutes or 2 hours later to see whether another small correction is needed. Sometimes yes, sometimes no.
That’s what works for me. Your results may be different.
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Hmmm… as some alternate data, I’ve never seen any difference between injecting an enormous bolus (say, 25U) all in one place, or breaking it up into 2 or 3. I experimented a lot with this after I first heard it, 'cause I like pizza 
Now, I’m always pretty slow with injections, imagining it helps the liquid spread in the tissue easier. I don’t know if that’s true or just some pizza-induced hallucination, but it works for me
'course, I pump these days so this is academic for me.
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I’m T1D, insulin resistant, eat lower carb and take 7 or more units almost all the time. I don’t split the dose or anything - just take it all at once. It doesn’t matter in my case, but as always what works for me doesn’t work for everyone.
I haven’t had a slice of pizza in four years. It would be at least 10 units for one slice. As my endo says, just take the amount of insulin you need.
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I’m fairly insulin resistant for a T1, but I eat moderate carb. My most frequent bolus is 8 units, which I do in one injection since I bruise easily and don’t want to have more bruises than necessary. I just don’t have enough real estate to rotate my injections if I had to do two injections for one meal regularly.
I do sometimes split my injection for pizza, though, as just one piece of pizza (trimming off the outer crust) and a beer requires 10 or 11 units. I probably have pizza once every month or two. Splitting the bolus into two injections seems to be absorbed faster for me than one large injection. I take the injections before eating, as the duration of action is 4-5 hours for me, even with the smaller injections.
Thank you all so much for sharing your experiences. It is from hearing and learning about your experiences that I don’t feel alone. I don’t know anyone in my circle of friends or family who use insulin. I have some very distant (both physical distance, and by relationship-relatives of in laws) relatives who take metformin, that’s it.
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1 unit or 15 units, it doesn’t matter it’s all going into one shot. I used to take 35 units of Lantus at a time. There’s no way I would split that into 5 separate injections.
I hear the 7 unit rule a lot, but I’ve never followed it. Has Dr. Bernstein ever published any papers testing his 7 unit rule? Or is it just based off his own, anecdotal evidence? As much as diabetes varies between people, it would seem odd to make up a static rule about dosages.
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This expands it a bit
THE LAW OF INSULIN DOSE ABSORPTION
If you do not take insulin, you can skip this section.
Think again of traffic. You’re driving down the road and your car drifts slightly toward the median. To bring it back into line, you make a slight adjustment of the steering wheel. No problem. But yank the steering wheel and it could carry you into another lane, or could send you careening off the road.
When you inject insulin, not all of it reaches your bloodstream. Research has shown that there’s a level of uncertainty as to just how much absorption of insulin actually takes place. The more insulin you use, the greater the level of uncertainty.
When you inject insulin, you’re putting beneath your skin a substance that isn’t, according to your immune system’s way of seeing things, supposed to be there. So a portion of it will be destroyed as a foreign substance before it can reach the bloodstream. The amount that the body can destroy depends on several factors. First is how big a dose you inject. The bigger the dose, the more inflammation and irritation you cause, and the more of a “red flag” you send up to your immune system. Other factors include the depth, speed, and location of
your injection.
Your injections will naturally vary from one time to the next. Even the most fastidious person will unconsciously alter minor things in the injection process from day to day. So the amount of insulin that gets into your bloodstream is always going to have some variability. The bigger the dose, the bigger the variation.
A number of years ago, researchers at the University of Minnesota demonstrated that if you inject about 20 units of insulin into your arm, you’ll get on average a 39 percent variation in the amount that makes it into the bloodstream from one day to the next. They found that abdominal injections had only a 29 percent average variation, and so recommended that we use only abdominal injections. On paper that seems fine, but in practice the effects on blood sugar are still intolerable. Say you do inject 20 units of insulin at one time. Each unit lowers the blood sugar of a typical 150-pound adult by 40 mg/dl. A 29 percent variability will create a 7-unit discrepancy in your 20-unit injection, which means a 280 mg/dl blood sugar uncertainty (40 mg/dl x 7 units). The result is totally haphazard blood sugars and complete unpredictability, just by virtue of the varying amounts of insulin absorbed. Research and my own experience demonstrate that the smaller your dose of insulin, the less variability you get. For type 1 diabetics who are not obese, we’d ideally like to see doses anywhere from ¼ unit to 6 units or at the most 7. Typically, you might take 3–5 units in a shot. At these lower doses, the uncertainty of absorption approaches zero, so that there is no need to worry about whether you should inject in your arm or abdomen or elsewhere.
I have a very obese patient who requires 27 units of long-acting insulin at bedtime. He’s so insulin-resistant that there’s no way to keep his blood sugar under control without this massive dose. In order to ameliorate the unpredictability of large doses, he splits his bedtime insulin into four small shots given into four separate sites using the same disposable syringe. As a rule, I recommend that a single insulin injection never exceed 7 units.
,
Many years ago, John Galloway, then medical director of Eli Lilly and Company, performed an eye-opening experiment. He gave one injection of 70 units of regular insulin (a very large dose) to a nondiabetic volunteer who was connected to an intravenous glucose infusion.
Dr. Galloway then measured blood sugars every few minutes and adjusted the glucose drip to keep the patient’s blood sugars clamped at 90 mg/dl. How long would you guess the glucose infusion had to be continued to prevent dangerously low blood sugars, or hypoglycemia?
It took a week, even though the package insert says that regular insulin lasts only 4–12 hours. So the conclusion is that even the timing of injected insulin is very much dependent upon how much was injected. In practice, larger insulin injections start working sooner, last longer, and have less predictable timing.
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I read that from Dr. B too. For a while I was splitting my doses but I quickly tired of turning 1 shot into 2-3, multiple times a day. I sometimes do 20U injections and don’t notice a problem with it. Maybe it hasn’t been a problem so far because I’m so terribly insulin resistant?
Everybody reacts differently to different things. Bernstein simply observed empirically that the larger the dose, the greater the chance of its behaving unpredictably. That doesn’t mean that every such injection will behave that way, nor that 7u is the magic number for each person. If 20u gives you good results, then it gives you good results. I wouldn’t worry about it.
I’m glad that it doesn’t seem to be a problem for you. I can definitely see that it could get tiresome turning 1 shot into 2-3. Imagine that, in addition to, split meal bolus because of slower digesting protein/fat.
I am learning that for some meals, I may have to bolus 2 to 3 times.
I am running into the same thing. Most days I struggle to tell if the problem was the wrong i:c ratio or just slow digestion. 
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or you need to do an overnight and miss a meal basal testing again, to get that right first
I tend to think it is the slow digestion because if my 2 hour numbers are fine and around the 4th hour, there may be a rise then I suspect slow digestion/fat/protein. If the I:C ratio were incorrect and I under bolused, I would think that my 2 hour, 3 hour and 4 hour BG would all be high. (I think most of the carb would have been addressed by the insulin by around 2 hours or 2.5 even if injection/food time were not well matched.) Does this logic make sense?
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I’ve checked around midnight,2 AM, 6 AM and skipped breakfast and checked around 11 AM, BG doesn’t vary by more than 30. I’ve had very late lunches after having had breakfast (6 hours since the last meal), BG looked steady. The only meal that I have not skipped is dinner. Because I use currently useTresiba once daily, even if my basal fluctuated during the day, I can’t really do much about it. I may try to change the time of my Tresiba dosing.
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