Lights! Camera! Insulin Action! MDI

Adjusting Insulin (MDI): how insulin action impacts blood glucose

If your child has predictable lows (or high BG), you may need to adjust their insulin doses. But which dose, and how much should you adjust by? You can start the process here by looking at how and when the action of long-acting insulin plus rapid-acting insulin affects BG in a Multiple Daily Injection (MDI) program.

Before Reading This Article...

Before making any changes to insulin doses, it is important to understand the action of insulin (the onset, peak and duration of different types of insulin). Therefore, as background for the information that follows, we recommend you first review Insulin Types & Action.

You may remember that:

    1. Conventional Program in which you give 3 injections of N/NPH and/or rapid-acting insulin
    2. Basal-Bolus Program with Multiple Daily Injections (MDI) in which you give 4 - 6 (or more) injections of long-acting plus rapid-acting insulin
    3. Pump Therapy program in which you infuse (rather than inject) rapid-acting insulin only.

On this page we are talking about MDI (#2).

  • Your child's current blood glucose (BG) is a result of several factors, including the way that a particular insulin behaves, which we call "insulin action." In other words, insulin action describes how quickly the insulin starts to affect blood sugar, when it peaks (has the most power), and how long the effect of the insulin lasts.
  • Long-acting insulin starts to work in 60-90 minutes, has no peak, and lasts 12-24 hours.
  • Rapid-acting insulin starts to work in 15 minutes, peaks at 1 hour, and lasts 3-5 hours.

For the discussion that follows, “long-acting” insulin refers to Lantus® or Levemir®; “rapid-acting” insulin refers to Humalog®, NovoRapid®, or Apidra

How Insulin Affects Blood Sugar in an MDI Program

This insulin action diagram for a Basal-Bolus insulin program (in which you deliver Multiple Daily Injections) shows that the blood glucose at a given time is affected by a certain previous insulin dose.  If we follow the curve back from breakfast, for example, we can see that it leads to breakfast the day before, when a dose of long-acting insulin was given. If we follow the rapid-acting curve back from supper, we can see that it leads to lunch. 

Mulitple Inbjections in an MDI (Basal-Bolus) Program
Mulitple Inbjections in an MDI (Basal-Bolus) Program

Another way of expressing this relationship is to say that:

  • Blood Glucose before breakfast tells you about how well the Morning dose of long-acting from the previous day (or bedtime long-acting, if applicable) is working.

  • Blood Glucose before lunch tells you about how well the morning dose of rapid-acting is working.

  • Blood Glucose before supper tells you about how well the lunch dose of rapid-acting is working.

  • Blood Glucose at bedtime tells you about how well the supper dose of rapid-acting is working.

Therefore, if the breakfast blood glucose is consistently out-of-range (high or low), you may want to change the morning long-acting insulin (or bedtime long-acting, if it’s delivered twice per day); if the lunch blood glucose is consistently out-of-range (high or low) you may want to change the dose of morning rapid-acting insulin.

Next Steps on adjusting insulin in a Basal-Bolus / MDI Program:

The above information was adapted with permission from The Alberta Children’s Hospital Diabetes Clinic information handouts.

The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.