What Is Rapid-Acting Insulin?

How It Works and What Kinds Exist

Woman holding insulin syringe
Tuomas Marttila / Getty Images

A rapid-acting insulin is one whose chemical structure has been changed so that the insulin is more quickly absorbed into the bloodstream. This change to the chemical structure of the insulin does not affect its ability to lower blood sugar (glucose) but it does affect the rate at which the insulin is absorbed. Rapid-acting insulin is absorbed into the bloodstream within minutes and has many potential benefits for people with diabetes.

Who Needs Rapid-Acting Insulin?

All people with type 1 diabetes and some people with type 2 diabetes need to take insulin in order to process the glucose from food.

In type 1 diabetes, this is because the pancreas no longer makes insulin. In type 2 diabetes, the pancreas makes insulin, but their bodies no longer respond as well to it, sometimes making injections of insulin necessary.

People with type 1 diabetes need to take both basal and bolus insulin. Basal insulin is the background insulin that is normally supplied by the pancreas and is present 24 hours a day, whether or not the person eats. Bolus insulin refers to the extra amounts of insulin the pancreas would naturally make in response to glucose taken in through food. The amount of bolus insulin produced depends on the size of the meal. Rapid-acting insulin is a type of bolus insulin.

Types of Rapid-Acting Insulins

There are currently three rapid or fast-acting insulins. The first is generically referred to as lispro but is marketed under the name Humalog and manufactured by Eli Lilly. Humalog is the oldest of the three rapid-acting insulins and has been commercially available since 1966.

A second rapid-acting insulin was approved by the U.S. Food and Drug Administration in 2000. This insulin carries the generic name of aspart but is marketed under the brand name NovoLog and is produced by Novo Nordisk.

Yet a third rapid-acting insulin was added in 2006. It is called insulin glulisine and is best known by its brand name Apidra. It is marketed by Sanofi-Aventis.

In 2015, another type of rapid-acting insulin became available in the U.S. It's an inhaled insulin by the brand name Afrezza.

How Rapid-Acting Insulin Works

All three of these rapid-acting insulins are quickly absorbed into the bloodstream and begin working within about 15 minutes. Each insulin reaches their peak potency in about one hour and continues to lower blood sugar for up to five hours. This quick absorption of the insulin allows a person to inject a rapid-acting insulin just before eating to “cover” the rise in blood sugar that occurs when food is eaten. The peak potency at one hour coincides with the time that glucose is typically peaking, offsetting the rise in blood sugar.

Onset, Peak, and Duration in Three Fast-Acting Insulins

Here is the difference in onset, peak, and duration between these types of rapid-acting insulins:

1. Brand name: Novolog (generic name: aspart):

  • Onset: 5-15 minutes
  • Peak action: 1-3 hours
  • Duration: 3-5 hours

2. Brand name: Apidra (generic name: glulisine):

  • Onset: 5-15 minutes
  • Peak action: 30 minutes-90 minutes
  • Duration: 3-5 hours

3. Brand name: Humalog (generic name: lispro):

  • Onset: 5-15 minutes
  • Peak action: 30 minutes-90 minutes
  • Duration: 3-5 hours

Rapid-Acting Insulin in Pumps

Rapid-acting insulin is also used in insulin pumps to provide a continuous but low level of insulin. This continuous flow of insulin is often referred to as basal insulin and is the ongoing insulin that is needed to manage normal fluctuations in blood sugar between meals and during sleep. Additional units of rapid-acting insulin are given at meal times (called bolus insulin) to offset the effects of rising glucose from the food you are eating.

Was this page helpful?

Article Sources

  • Hieronymus, L. M.S.Ed., A.P.R.N., B.C.-A.D.M., C.D.E., Geil, P. M.S., R.D., C.D.E. "Types of Insulin. " Diabetes Self-Management, 2009.
  • Insulin. American Diabetes Association. " Consumer’s Guide 2011. " Diabetes Forecast, January 2011, Vol, 64, No. 1.