Insulin Replacement Therapy

Insulin replacement therapy and type 1 and 2 diabetes

Type 1 diabetes (also called insulin-dependent diabetes) is an autoimmune disease in which the body's immune system attacks the cells that produce insulin, resulting in no, or a low amount of, insulin. Type 1 diabetes usually occurs at a younger age, with onset often before the age of 30. Treatment for type 1 diabetes includes daily injections of insulin.

Type 2 diabetes is typically a result of the body's inability to make enough of, or to properly use insulin. Treatment often begins with an exercise program and a healthy diet to help lower the blood sugar levels. However, if this treatment plan is ineffective, medication may be necessary. Medications for diabetes may be given in pill or injectable forms.

What is insulin?

Insulin is a hormone produced by the pancreas that helps lower the blood sugar by moving sugar from the bloodstream into the cells of the body. Once inside the cells, blood sugar becomes the essential source of energy for the body.

What are the different types of insulin?

There are four types of insulin, classified according to the following:


How quickly the insulin starts to work after it is injected

Peak time

The period of time when the insulin is most effective in lowering blood sugar levels


How long the insulin remains working in the body

Insulin may act differently when administered to different individuals, so the times of onset, peak time, and duration may vary. The four types of insulin include:

Insulin type


Peak time


Rapid acting, Lispro, Aspart, Glulisine insulin

15 minutes

30 to 90 minutes

3 to 5 hours

Short acting, Regular (R) insulin

30 to 60 minutes

2 to 4 hours

5 to 8 hours

Intermediate acting, NPH (N) or Lente (L) insulin

1 to 3 hours

8 hours

12 to 16 hours

Long acting, Glargine, Detemir insulin

1 hour


20 to 26 hours

Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Some people with diabetes may have to take a combination of two different types of insulin to control their blood sugar levels. Some insulin can be purchased already mixed together, such as Regular and NPH insulin, to allow for injection of both types of insulin at the same time. Other types of insulin cannot be mixed together and may require two separate injections.

Insulin is manufactured at different strengths; U-100 insulin (100 units of insulin per milliliter of fluid) is the most common strength. The syringes for administering insulin are specifically designed for each different strength. Therefore, a U-100 syringe can be used only with U-100 insulin.

The type of insulin chosen may reflect the person's preferences and ability to adhere to any given treatment regimen. Other factors include an individual's:

  • Willingness to monitor blood sugar levels regularly
  • Daily activity levels (type and amount of exercise)
  • Understanding of diabetes
  • Stability of blood sugar levels
  • Diet

How is insulin administered?

Insulin has to enter the body's bloodstream to be effective. This is accomplished through injections into the fat layer, usually in the arm, thigh, or abdomen. Different sites on the body allow the insulin to enter at different rates. Insulin injected into the abdominal wall works the fastest, whereas injection into the thigh works the slowest. Insulin must be administered to the body via an injection and cannot be taken by mouth because it is destroyed in the stomach during digestion.

The timing of insulin injections is very important. Insulin usually needs to be administered before mealtimes--before sugar from a meal starts to enter the bloodstream. Always consult your doctor concerning your individual insulin treatment, including injection sites, dosage, frequency, and specific times of administration.

What are the different types of insulin injection devices?

There are many types of insulin injection devices available. Some examples of devices include:


The syringe is the most common device used to administer insulin. The needle of the syringe is placed under the skin, and the insulin is injected.

Insulin pen

Often used for multiple, daily doses of insulin, the insulin pen holds a cartridge with insulin. The pen, which looks like a writing pen, has a small needle at the tip. A dial on the pen allows the user to set the appropriate dosage. A plunger on the other end of the pen is used to actually deliver or inject the insulin.

Insulin jet injector

An insulin jet injector looks like a large pen. The injector uses a mechanism to produce high-pressure air to "spray" the insulin through the skin. Insulin jet injectors may be an option for people who do not tolerate needles.

External insulin pump

An insulin pump is a device that pumps insulin continuously through plastic tubing attached to a needle under the skin near the abdomen. The pump is small enough to be worn on a belt or in a pocket.

Oral insulin

Because insulin is quickly broken down during the digestive process, it has historically been given by injection, usually just under the skin. However, new pharmaceutical materials and techniques have been developed that can protect insulin from being broken down in the digestive tract.

The first human trials of oral insulin were reported in 2006. Phase I clinical trials have shown insulin given in a gel capsule to be safe and effective. Clinical trials will continue over the next several years as the medication moves through the federal approval process.

Pancreas transplantation

In type 1 diabetes, the pancreas produces too little insulin or none at all. Thus, replacing a nonfunctioning pancreas with a healthy transplanted pancreas would seem to be a cure for type 1 diabetes.

In the 1960s, pancreas transplantation was first attempted. However it was not until the improvement of surgical techniques and the introduction of new anti-rejection medications years later that pancreas transplantation became a realistic potential treatment for type 1 diabetes. Pancreas transplantation continues to be studied at many centers in the U.S. and around the world.

When successful, a pancreas transplant cures diabetes. Blood sugar levels become normal because the new pancreas produces insulin. However, as with most types of solid organ transplantation, a number of complications may occur. The most common complications include rejection of the new organ, infection, and adverse effects from the antirejection medications that must be taken indefinitely after transplantation.

There are three types of pancreas transplants:

  • Simultaneous pancreas and kidney transplant (SPK). Because most people with type 1 diabetes who meet the criteria for pancreas transplantation also have some degree of kidney disease, simultaneous transplantation of both a pancreas and a kidney is often performed. The best success rates have been achieved with this type of procedure. 
  • Pancreas after kidney transplant (PAK). In this procedure, a pancreas is transplanted into a person who has already received a kidney transplant. This procedure generally has a success rate near that of SPK procedures.
  • Pancreas transplant alone (PTA). In this procedure, only the pancreas is transplanted. This type of procedure is done less often, and generally has a lower success rate than the other procedure types.

Pancreas islet cell transplantation

The islet cells in the pancreas produce insulin. Only about 1 to 2 percent of the cells in the pancreas are islet cells.

In the 1970s, research into islet cell transplants in mice was very successful. However, translating this success into human islet cell transplantation was initially difficult. Researchers at the University of Alberta in Edmonton, Alberta, Canada, developed a specialized protocol for islet cell transplantation that shows great promise. Research continues on the Edmonton Protocol, in a multicenter trial being conducted by the Immune Tolerance Network. Sponsors for the Immune Tolerance Network are the National Institute of Allergy and Infectious Disease, the NIDDK, and the Juvenile Diabetes Foundation.

Islet cell transplantation is a noninvasive procedure (no surgical incision is required). Islet cells are taken from a donor pancreas and then injected into the recipient's liver through a catheter (long, thin tube). Once the islet cells have been implanted in the donor, they begin to produce and release insulin.

People who receive an islet cell transplant must take antirejection medication for the rest of their lives.

Insurance and insulin pumps

Medicare has covered the cost of insulin pumps since 1999. Recent changes to the Medicare policy relax the eligibility for coverage based on fasting serum C-peptide levels (a blood test that measures the amount of C-peptide in the blood; C-peptide is a subunit of insulin). Under the revised policy, more people are eligible to receive Medicare coverage for insulin pumps. Always check with your insurance company and the most recent Medicare guidelines to determine if insulin injection devices and supplies are covered under your plan.