“Insulin” is commonly used as a generic term for a multitude of different types of insulin that are available. When you shop for a new “car,” you may come home with an SUV, a pick-up truck, a sports car, a sedan, or a minivan. All these different “cars” have a different function, just as different types of insulin have different effects.
Insulin has been used since the 1920s in the treatment of diabetes. Initially, purified pork and beef insulins were utilized; however, patients could develop antibodies or symptoms of an allergic reaction to these “foreign” substances. Consequently, human insulin was developed for pharmaceutical use in the 1960s. The 1990s saw the development of genetically altered “analog” insulins; these have become the standard of care today.
When considering insulin therapy, we need to look at these three factors:
- The onset of action of the insulin, meaning how quickly does the insulin begin to work?
- The duration of action of the insulin, meaning how long does the insulin work?
- When does the insulin peak, meaning when is the insulin working its hardest?
We place insulins into four categories, based on how long they are effective. These categories include:
- Rapid-acting insulins have an onset of action within 15 minutes, peaking in 1 to 2 hours with a duration of 3 to 4 hours.
- Short-acting insulins have an onset of action in 30 to 60 minutes, peaking in 2 to 3 hours with a duration of 4 to 6 hours.
- Intermediate-acting insulins have an onset of action in 4 to 6 hours, peaking in 10 to 12 hours with a duration of 14 to 18 hours
- Basal (or baseline) insulins are long-acting, with an onset of action in approximately one hour. They are characterized as “peakless” insulins, but truly have a small peak at approximately 10 hours, with a duration of up to 24 hours.
A number of premixed insulins are also available on the market. They are combinations of either rapid- or short-acting insulin with intermediate-acting insulin. The three combinations available include:
- 25% rapid-acting insulin and 75% intermediate-acting insulin
- 30% rapid- or short-acting insulin and 70% intermediate-acting insulin
- 50% rapid-acting insulin with 50% intermediate-acting insulin
The older human insulins that are still available and used today are short-acting and intermediate-acting insulin. These human insulins vary significantly in their day-to-day action within the same person, producing a higher incidence of hypoglycemia. Their peak is such that it requires the patient be eating at the time of peak action to prevent the onset of hypoglycemia. I limit the use of these insulins, believing that the patients who take them are “working for their insulin,” rather than “having their insulin work for them”.
The newer analog insulins have much less variability from day-to-day. They are often used in basal-bolus therapy, or what I like to refer to as “baseline-mealtime dosing with multiple daily injections.” This will generally require four or more injections a day in order to control before- and after-eating glucoses with a much lower incidence of hypoglycemia than the older insulins.
