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  What is Insulin?

Overview

Insulin is a hormone produced by beta cells in the pancreas. It has three important functions:1

  1. Allow glucose to pass into cells, where it is used for energy.
  2. Suppress excess production of sugar in the liver and muscles.
  3. Suppress breakdown of fat for energy.

In the absence of insulin, blood sugar levels rise because muscle and fat cells aren't able utilize glucose for energy. They signal the body that they're "hungry." The liver then releases glycogen, a form of stored glucose. This further increases the blood sugar level. When the blood sugar level reaches about 180 mg/dl, glucose begins to spill into the urine. Large amounts of water are needed to dissolve the excess sugar, resulting in excessive thirst and urination.

Without glucose for energy, the body begins to metabolize protein and fat. Fat metabolism results in the production ketones in the liver. Ketones are excreted in the urine along with sodium bicarbonate, which results in a decrease in the pH of the blood. This condition is called acidosis. To correct the acidosis, the body begins a deep, labored respiration, called Kussmaul's respiration. Left unchecked, a person in this situation will fall into a coma and die.

Common Questions

Why do I have to inject insulin?
Insulin must be injected because it is a protein. If it were taken orally, the body's digestive system would break it down, rendering it useless.


Where should I store insulin?
Unopened insulin vials should be kept cool. Storing them in the refrigerator will help them last as long as possible. Never freeze insulin however, as it can destroy it. Open insulin, whether vials or pens, can be kept at room temperature for about a month.


Where does insulin come from?
Insulin used by people with diabetes can come from three sources: human (created via recombinant DNA methods), pork, or beef. Beef insulin is being discontinued, and most newly diagnosed diabetics are placed on human insulin.


What kinds of insulin are there?
Insulin is classified according to how long the insulin works. There are several types of insulin, listed here in order of rate of action. Be aware that duration of insulin action varies by individual, activity level and location of injection.

Types and Duration of Action of Insulins Available in the United States

Type of Insulin
(Trade Names)
Supplier Appearance Begins Working Peak Activity All Gone
Short Acting
[RECOMMENDED!] Humalog® (insulin lispro) Eli Lilly Clear 10 - 15 minutes 30 - 60 minutes 4 hours
[RECOMMENDED!] NovoLog® (insulin aspart) Novo Nordisk Clear 10 - 15 minutes 30 - 60 minutes 4 hours
[RECOMMENDED!] Apidra® (insulin glulisine) Sanofi Aventis Clear 10 - 15 minutes 30 - 60 minutes 4 hours
Regular
(Humulin, Actrapid, Velosulin®)
Eli Lilly and Novo Nordisk Clear 30 minutes 2 - 4 hours 4 - 8 hours
Intermediate Acting
NPH
(Insulatard®)
Eli Lilly and Novo Nordisk Cloudy 2 - 4 hours 6 - 8 hours 12 - 15 hours
LENTE®
3 parts Semilente to 7 parts Ultralente
Eli Lilly and Novo Nordisk Cloudy 1 - 2 hours 6 - 12 hours 18 - 24 hours
Long Acting
[RECOMMENDED!] Lantus (insulin glargine) Sanofi Aventis Clear 4 - 6 hours No peak 24+ hours
[RECOMMENDED!] Levemir (insulin detemir) Novo Nordisk Clear 3 - 6 hours 6 - 15 hours (gentle) 18 - 24 hours
ULTRALENTE® Eli Lilly and Novo Nordisk Cloudy 4 - 6 hours 8 - 15 hours 18 - 24 hours
Pre-Mixed (Action Varies)
NPH/Regular
70/30 or 50/50 are common mixes
Eli Lilly and Novo Nordisk Cloudy 30 minutes Varies 18 - 24 hours
Humalog Mix 75/25
75/25
Eli Lilly Cloudy 10-15 minutes Varies 12 - 15 hours
NovoLog Mix 70/30
70/30
Novo Nordisk Cloudy 10-15 minutes Varies 10 - 12 hours

Adapted from Understanding Insulin-Dependent Diabetes, 10th Edition by H. Peter Chase, M.D. and drug company data.

Production of Insulin in the Body

The creation of insulin in the beta cells of the pancreas is a two step procedure. Beta cells first produce preproinsulin. Preproinsulin is cleaved to create proinsulin, which is further cleaved to produce equal amounts of insulin and C-peptide. Endogenous (self-produced) insulin has a half-life of about four minutes in the bloodstream. C-peptide lasts about 30 minutes. By measuring the amount of C-peptide in the blood, scientists can determine the amount of insulin produced by the pancreas.2

In non-diabetics, the pancreas stores about 200 units of insulin. The average basal rate for adults is one to two units per hour. After meals, secretion increases to four to six units per hour.3

For More Information

  1. Clinical Data
    1. Insulin questions and insulin analog questions from the Diabetes Team
    2. Clinical Practice Recommendations: Insulin Administration by the American Diabetes Association
    3. How Long Should Insulin Be Used Once a Vial Is Started?
    4. Avoiding Insulin Errors. Also available in PDF format.
    5. Insulin errors--abbreviations will get U in trouble examines the importance of double-checking your insulin vials.
    6. Insulin from Insulin-Dependent Diabetes in Children, Adolescents and Adults by Ragnar Hanas, M.D.
    7. The 1500 Rule shows how far your blood sugar is likely to drop per unit of short-acting insulin
    8. Beef Insulin FAQ from the FDA has information about importing beef insulin for personal use
    9. Insulin: The Facts by the Canadian Diabetes Association
    10. The Protein Data Bank has a 3-D graphical view of an insulin hexamer.

  2. CME Courses Related to Insulin
    1. Advances in insulin therapy
    2. Optimizing insulin regimens in type 1 diabetes
    3. Novel insulins and strict glycemic control
    4. The changing model of insulin use in type 2 diabetes

  3. Industry Links
    1. Lantus time activity profile
    2. Time Activity Profiles of Novo Nordisk insulins
    3. Time Activity Profiles of Lilly insulins

  4. Other Links
    1. The Discovery of Insulin explores the work of Canadians Banting, Best, Colip and Macleod
    2. The History of Insulin, part of the Diabetic Medical Equipment History web site, offers an overview of the history of insulin.

References

  1. Understanding Insulin-Dependent Diabetes, 10th Edition by H. Peter Chase, M.D.
  2. Management of Diabetes Mellitus: Perspectives of Care Across the Life Span edited by Debra Haire-Joshu, MSEd, MSN, PhD, RN.
  3. Time Activity Profiles of Lilly insulins
  4. Time Activity Profiles of Novo Nordisk insulins

Foot Notes

  1. Understanding Insulin-Dependent Diabetes, 10th Edition by H. Peter Chase, M.D., 2002. See Insulin Activities table.
  2. Management of Diabetes Mellitus: Perspectives of Care Across the Life Span edited by Debra Haire-Joshu, MSEd, MSN, PhD, RN., St. Louis, 1992, pp. 120-121.
  3. Ibid.


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Last Updated: Mon Mar 27 15:27:46 2006
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