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).
NPH insulin (intermediate acting insulin which usually peaks in 6-8 hours) and works for 10-12 hours.
Insulin Glargine (Lantus) works for 24 hours and is relatively peakless.
Insulin Detemir (Levemir) works for 12 hours and is relatively peakless (some studies report that Levemir may work longer than 12 hours).
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).
Regular insulin-fast acting (starts working in about 30 minutes, peaks in 3-4 hours, and lasts 4-6 hours).
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).
Conventional insulin therapy: 2 shots/day
Conventional insulin therapy: 3 shots/day
Modified Basal Bolus therapy
"True" or Classic Basal Bolus therapy
Insulin Pump therapy
In conventional insulin therapy, NPH is used as a basal insulin and regular or analog insulin is used as a bolus insulin. These insulins can be mixed together or given separately via insulin pen. In these regimens, three meals and two- three snacks are usually required and carbohydrate counting is recommended to allow for consistent carbs at meals and snacks.
In "modified" basal bolus therapy, Lantus (usually one shot/day) or Levemir (usually two shots/day) is used as basal insulin. Analog insulin (novolog, humalog, or apidra) is given before meals (sometimes during or after, but preferably before) to cover the carbs in the meals or snacks. Lantus and Levemir do not cover carbohydrates and injections of analog insulin must be given to avoid hyperglycemia. Generally, fixed doses of analog insulin are given to cover meals (and sometimes snacks).
In "true" or classic basal bolus therapy, Lantus or Levemir is used as basal insulin. However, analog insulin is given before meals based on the amount of carbohydrates consumed and blood sugar amount. Hence, there is more flexibility in true basal bolus therapy in which an insulin to carbohydrate ratio and correction factor (insulin sensitivity factor) are used to determine the amount of analog insulin required. Accurate carbohydrate counting is essential and generally most families are required to attend classes to learn how to use "true" basal bolus therapy safely and successfully. Lantus and Levemir cannot be mixed together with rapid acting insulin. Each type of insulin is usually given by syringe or pen. In addition, Lantus, Levemir, humalog, novolog and apidra (vials or pens) must be disposed after 30 days of use.
Lastly, insulin pump therapy combines basal and bolus therapy with one rapid acting insulin (humalog, novolog, or apidra). In this situation, insulin is delivered continually in "units/hr" as basal insulin and bolus insulin is delivered by the pump (after buttons are pushed or via PDA) usually when the pumper consumes carbohydrates and/or the blood glucose needs to be lowered. Once again, carbohydrate counting is mandatory for insulin pump therapy. Children's National Medical Center currently offers the following pump choices based on the child/teen and parent preferences: ANIMAS, METRONIC MINIMED, OMNIPOD, and SPIRIT. As you may now know, the DELTEC COSMO pump has been discontinued. However support for those currently using the pump is still available.
Should you have any further questions about insulin, application, choices etc. please do not hesitate to reply by comment or via e-mail. I am happy to explain further to ensure that everyone understands how all the different types of insulin work.