After reviewing the healthcentral web site and diabetes related links, I noticed that questions about the different types of insulin and how they work continue to be a popular topic. As an associate professor of Pediatrics at the George Washington University School of Medicine and Health Sciences, I have the responsibility of teaching third year medical students and pediatric residents at Children's National Medical Center about the treatment of childhood diabetes. Understanding the different types of insulin and how they act is essential in learning how to care for and manage diabetes. The most appropriate way to teach insulin and action is to understand how the pancreas secretes insulin.
The beta islet cells in the pancreas produce insulin. In the fasting state, small amounts of "basal" insulin (or continuous insulin) is released steadily by the pancreas to enable glucose to be transported to cells for energy. During a meal, the pancreas releases a "bolus" of insulin to cover the carbohydrates consumed. Therefore, basal and bolus insulin are both required to mimic the normal functioning of the pancreas.
At present, there are three types of "basal" insulin on the market (including combinations).
1. NPH insulin (intermediate acting insulin which usually peaks in 6-8 hours) and works for 10-12 hours.
2. Insulin Glargine (Lantus) works for 24 hours and is relatively peakless.
3. Insulin Detemir (Levemir) works for 12 hours and is relatively peakless (some studies report that Levemir may work longer than 12 hours).
4. Combinations of NPH--typical examples: Insulin 70/30 (70 percent NPH, 30 percent Regular insulin), Insulin 70/30 mix (70 percent delayed release aspart and rapid acting aspart novolog)
Likewise, there are four types of "bolus" insulin on the market (including combinations as mentioned above).
1. Regular insulin-fast acting (starts working in about 30 minutes, peaks in 3-4 hours, and lasts 4-6 hours).
2. Analog insulin (rapid acting)
a. Insulin Lispro (humalog) begins working immediately, peaks in about 1.0-1.5 hours, and lasts about 3-4 hours
b. Insulin aspart (novolog) begins working immediately, peaks in about 1.0-1.5 hours, and lasts about 3-4 hours
c. Insulin glulisine (apidra) begins working immediately, peaks in about 1.0-1.5 hours, and lasts about 3-4 hours.
Each manufacturer notes slightly different times of peaking and duration based on clinical studies. Most analog insulin users note little clinical difference among the three analogs; however, in some people there are significant differences in peaking, duration, and effectiveness.
A combination of basal and bolus insulin is usually begun on all patients with insulin dependant diabetes (with the exception of the insulin pump in which rapid acting insulin is used as both basal and bolus insulin). There are generally five general types of insulin regimens (see previous blogs).