Length of fast acting insulin

I have been on a pump vacation for a few days now. Thought I had adjusted my long acting insulin to where everything would be fine. Went low in the mid afternoon 3 days in a row.Figured it was time to do a basal test.

Woke up with bg at 130, took 3 units of novolog at 6:20 and ate 50 carbs (1:25 plus correction) at 6:50. Using dex I tracked that by My blood sugar kept dropping well after noon. I was about to chalk this up as too much basal when around 1:15 it leveled off at 75. Then it stayed at 75 for the next 3 hours. Is it possible that my morning shot at 6:20am affected my sugar for 7 hours? If that's the case of course I'm going low because my lunch is an early one, and I take my bolus at 11:00am. I assumed I was stacking a little, with a 4-5 hour insulin life, but if it's truly lasting until 1:20pm, I'm probably stacking onto 25% leftover from morning bolus.

I am still early in this, and my TDD is between 15-20 units per day. Would being more sensitive to insulin make it last longer as well? Just would like to see if anyone's last longer in them to validate my case.


Usually fast acting is 4 hours. I am pretty normal, but it varies from person to person.

I would check hourly on a "normal" (ha ha) day and see the rise and fall.

Basal testing is not big here, and I do not do it often, but when starting out it can really help you see the levels--record and look.

Usually, in my mind, the more insulin you require, the less likely that you are more sensitive. When I was first diagnosed in 1962, I took over 150 units per day (I know, different time, different insulin) but I now dose about 12 units of novolog per day. It can all change.....

Yeah, I know the normal limits on fast acting. But I have viewed in the past that my bg tends to keep dropping well after the "4 hour rule". I was just wanting to see if anyone has noticed theirs keep dropping in the 6+ hour range ever. I have seen this on me multiple times (or at least close to 6 hours, this is the first for a 7 hour drop), so just wanted to hear from others that might do this.

Insulin is depleted on a bell curve, it's not linear. Example: If your insulin lasted four hours you would have about 5-10% left in three hours ...not 25%. And yes insulin will lasts 5-6 hours but on a pump the duration setting is a way to increase or decrease correction insulin so it has a impact on target numbers. A pump may work better set at 3 hours when in fact the insulin is actually lasting 5-6 hours.

I can make corrections at 2 hours without any fear of stacking because my pump assumes my BG at 2 hours post meal bolus is 130mg/dL not 90mg/dL....these calculations are hard to make when on MDI, it's hard to track IBO.

Hi John - it's actually not like a bell curve. If you want a big picture idea of what the curves look like, please see ManageBGL.com. It plots the insulin profile curves and you can easily see stacked insulin etc.

Hi Benjamin,

Insulin action time varies widely, all sorts of physiological factors, with heat and exercise reducing it. My daughter (8 years old) has an action time of around 6 hours, mine is around 3.

If you've just got back to MDI, try ManageBGL.com - it can help you understand where things are going wrong, especially with multiple insulins, varying ratios and timing and size of meals, and the active insulin tracking is algorithmic (ie calculated) rather than buckets for hour 1 (15%), hour 2 (45%).. etc

These look like bell curves to me....???

Yes you guys win, technically the gaff shows skewed distributions.