How do I know whether my prebolus is right?

I recently swtiched over from apidra to novorapid because I went onto the tslim pump and it doesn’t like apirdra.

According to this the novarapid instructions,

“NovoRapid should be given immediately before a meal because of the fast onset of action (start of the meal should be not more than 5-10 minutes after injection).”

How do I know whether my wait time is right? Say if my BS starts to peak 10-15 mins after a meal and peaks at the 1 hour mark, is waiting 10 minutes enough of a head start?

If my blood sugar is out of range at the 1 hour mark, how do i tell whether its because its a prebolus timing issue or a bolus not enough issue?

You just need to experiment a little and figure out when it hits you.
If you have cgm this is easy. If not you can take fingersticks every 5 min until you see your sugar start to go lower


Thanks, it sure does sound easier with cgms! So is the rule of thumb as soon as its trending down, that’s when I can eat?

And maybe I also have to account for my BG at the time I prebolus too? If I’m sitting at 6mmol (100mg) I should be right to eat when it starts trending down, but if I’m sitting a 12 mmol(200mg) then I should probably wait until it drops to 6mmol (100mg)? Is this thinking on the right path?

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Yes to all of the above :grinning:.


I wait to prebolus until I am in my preferred range. For my standard meal, I prebolus half my dose a half hour before I eat and the rest when I eat because that allows me to make the final bolus adjustment to what I actually ate. But for someone else a half hour could be too long, or half the dose early could be too much. This does depend what I have decided to eat. If it’s high fat I am more likely to wait to bolus until I eat and maybe some a half hour after. If it’s just fruit then I am taking most of my insulin early. So yes, it takes some experimenting to learn what works for you.

But if I wait until I see an arrow trending down, the food I am eating won’t digest in time for when the insulin really hits. Unless I am starting out at a higher than my normal level.


In my experience, Apidra is slightly faster onset than Novolog (Noivorapid), has shorter tail, and is about 80% efficacy (meaning I need more units Apidra than with Novo for the same carbs). I pre-bolus with both, longer if I’m higher to start, and depending on what food. Just surf your cgm and you’ll be fine. It takes practice.

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This is essentially what I do, too… But I use my pumps extended bolus for it. I try to pre-bolus 15-30 minutes before the meal, but really it’s just when I remember to. I set the units I’m likely to need, tell the pump to deliver a fraction of it now (anywhere from 10-75% based on where my sugar currently is and a little educated guess as to how fast the meal will hit me), and I set the rest to extend for up to an hour, basically for 30 minutes after I intend to start eating. If I wind up not eating enough, I just cancel the remaining bolus.

This was actually my husband’s brilliant suggestion/urging, because he got tired of me complaining about HAVING to eat more if my stomach turned sour, or something.

It sounds way more complicated trying to explain than it really is. In reality I just quick-bolus a little or a lot based on an educated guess, then set an extended bolus when I sit down to actually eat.


This is a good idea as it can resolve the issue of not eating enough.

I have another question - if I am running into a hypo state, should I pre bolus before eating. If I’m in hypo state and my hypo symptoms are kicking in then I’m just going to eat straight away but I’m talking about sugar being low but hypo symptoms have not kicked in yet.

I’ve always been told treat the hypo first. But if I don’t prebolus then I’m surely going to go high after each hypo isn’t it?

Ive previously been on apidra and there was very little prebolus required so has never been an issue. But I’ve switched to novorapid recently hence why I have all these prebolus questions :sweat_smile:.

This prebolus is a pain I should add, I’ve had a lot more hypos after bolusing because I’ve missed eating at the right time. When you are in the middle of something and think an extra five minutes won’t hurt because you don’t feel any hypo symptoms at that time, only to find hypo symptoms kicking in after you start eating isn’t the best feeling in the world :unamused:

@truenorth - I’m thinking of trying some Apidra. How does its onset speed compare to Fiasp?

I’ve never used Novorapid, but I understand the 30 minute onset is similar to Humalog

@Jimi63 I tried Apidra years ago and didn’t notice anything different about it than Humalog in speed of working for me. What it did do is have a stronger kick hours later that threw me off.

This was at the time though that I was misdiagnosed and on too strong a dose of Lantus, no guidance and trying to figure out how to manage blood sugars. So it’s hard to completely know what it would have done under better management.

I am one that fiasp turns to water with more than one use a day or more than one day in a row.

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Thanks Marie - I’m looking for alternatives as I’ve developed insulin resistance to both my go to (Fiasp) as well as Humalog.

@Jimi63 I’ve been on apidra for over 10 years and I’ve rarely had to prebolus. I usually take it within 5 minutes of eating. From what I read fiasp is super quick acting, quicker than apidra.

I only switched to novorapid recently because apidra is notorious for causing occlusions on the tslim pump - I’ve tried it myself and it blocked up on the second day! If I had the choice, I would pick apidra over novorapid due to the fact I don’t need to time the prebolus. On the surface of things, they seem to work the same (other than the prebolus), I was able to switch over with little to no adjustment in dosage. I say on the surface because I’m still working out whether novorapid behaves differently to apidra in terms of sensitivity and timing. I switched over end of July 2020.

Maybe you can trial apidra, your DE or endo or GP May have a sample for you to trial. But if you are on a tslim pump, it’s a no go. I was pumping using apidra for 8 years on the Medtronic. I didn’t get any occlusions for 4 years and then they started happening… I didn’t think it was the apidra causing it since I didn’t get it for the first four years and the company sanofi assured me there was no change in the formula. So I just narrowed occlusions down to scarring of tissues due to years of pumping.

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Thanks @tedos

I was aware of the Apidra pump occlusion issues, many people experienced the same thing with Fiasp. It has been suggested that Fiasp & Apidra react with the plastics used in Medtronic and Tandem pump lines.

I ran Fiasp in a Medtronic pump for the better part of 9 months with no occlusions, but I change out the lines and site sets religiously every 72 hours.

If the Apidra caused issues I’d just pump Humalog as basal and bolus MDI with Apidra.

In Canada we don’t require a prescription for insulin, so next time I’m at the pharmacy I’ll pick up a vial of Apidra and give it a try.


Apologies for delayed reply. How did it work out?

I haven’t used Fiasp. Truthfully, there are relatively small differences (for me) between Humalog, Novolog and Apidra, but even so sometimes those differences can have outsize advantages for certain foods and situations, maybe especially for an MDI user like me.

@truenorth I’m picking some Apidra up today on my weekly drug run. I’ll let you know how it works for me vs Humalog and Fiasp