An Insulin Primer

Until the twentieth century, type 1 diabetes was a fatal disease. Once we came to understand how insulin works in the body, however, everything changed. The discovery of the role of insulin was a group effort by people who didn’t know each other, but built on each others’ work. In 1869, a German medical student named Paul Langerhans figured out the regulatory role of insulin in the mammal body. In honor of his efforts, his name was given to the islets of Langerhans, where insulin is synthesized within the beta cells of the pancreas. Other Europeans and North Americans made important advancements right up until January 23, 1922, when a 14-year-old boy who was dying of diabetes at Toronto General Hospital was given the first successful injection of cow insulin.

Purified animal-sourced insulin was the only type of insulin available to people with diabetes until breakthroughs allowed the first genetically engineered “human” insulin to be produced in 1977. Genentech partnered with Eli Lilly, and in 1982 they sold the first commercially available biosynthetic human insulin, called Humulin. Today, nearly all of the insulin used worldwide is biosynthetic recombinant “human” insulin or its analogs.

Insulin Terms

Basal denotes a low, continuous delivery of insulin (either as a basal rate from an insulin pump or as an injection of long-acting insulin).

A bolus is a dosage of insulin intended to “cover” a meal or to make a high glucose level correction.

Kinds of Insulin

Rapid-acting insulin

  • also called lispro (Humalog), aspart (Novolog), or glulisine (Apidra)
  • begins to work immediately after injection
  • is most effective after approximately one hour
  • is usually taken just before mealtime (do not delay eating after taking rapid-acting insulin)

Short-acting insulin (human)

  • also called regular
  • typically reaches the bloodstream 30 minutes after injection
  • takes longer to work and keeps working longer
  • a higher dose of regular insulin usually works longer

Intermediate-acting insulin (human)

  • also called NPH or Lente
  • reaches the bloodstream 2 to 4 hours after injection
  • peaks 4 to 12 hours later and is generally effective for 12 to 18 hours
  • is combined with another substance that helps it work more slowly
  • can last as long as 18 hours

Long-acting insulin

  • also called, glargine (Lantus), or detemir (Levemir)
  • is commonly taken early in the morning or at bedtime
  • begins working 2 to 4 hours after injection
  • can last for up to 24 hours (copies natural basal insulin)
  • cannot be mixed with other insulin
  • should be taken around the same time each day
  • should not be administered intravenously.
  • insulin detemir is considered to have a shorter duration than insulin glargine

Pre-mixed insulin

  • can be used by people who mix NPH and regular insulin in a single syringe
  • especially useful for those with vision or dexterity problems

Many people use a combination of rapid acting or short-acting insulin with insulin glargine or insulin detemir. Because the long-acting insulins glargine and detemir are basal insulins that don’t cover meals, an injection of rapid-acting or short-acting regular insulin must be taken with every meal to provide bolus coverage for food intake. Unfortunately, it’s possible to mistake basal for bolus insulin, and Diabetes Health has written numerous times about close calls that people have experienced when they accidentally took the wrong insulin. Luckily, products are available that distinguish the vials from each other, such as color and shape-coded vial “cozies,” and manufacturers are beginning to make the packaging more distinct. 


Insulin is sold dissolved or suspended in liquids. The solutions have different strengths. The most commonly used strength in the United States is U-100. That means the insulin has 100 units of insulin per milliliter of fluid. U-500 insulin is five times more concentrated than U-100.

Storing Insulin

Manufacturers recommend that insulin vials be stored in a refrigerator when they are unopened. Store open vials and pens at room temperature and discard per manufacturers directions.You should never store insulin in the freezer, direct sunlight, or your car’s glove compartment. The American Diabetes Association (ADA) recommends that you check the product label to see how long your insulin vial or cartridge can be used after the seal is broken. This depends on the type of insulin and how it’s packaged: in a vial or in a pen/cartridge system. Pre-filled insulin pens offer a portable and accurate alternative to vials and syringes and can be especially helpful to people who have poor eyesight or dexterity.

The ADA also recommends the following:

  • Before you use any insulin, check the expiration date. Don’t use any insulin beyond that date.
  • Examine the bottle closely to make sure it looks normal before you draw the insulin into the syringe
  • If you use regular, insulin aspart, insulin lispro, insulin glargine, insulin glulisine, or insulin detemir, make sure it is clear. There should not be any particles or discoloration.

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Get Acquainted with Insulin Pens
Injecting insulin with a vial and syringe can be inconvenient and difficult, but there is a simpler way to administer those multiple daily injections. An insulin pen can help you follow your insulin course of therapy more closely and achieve better diabetes control.

Why don’t more people use insulin pens?

Although insulin pens are very popular in Europe, fewer than 20 percent of Americans who inject insulin currently use pens.

A report published in Diabetes Care in November 2007 discussed the factors that affect the use of insulin pens by type 2 diabetes patients. The researchers studied 300 type 2 patients who used a vial and syringe to inject insulin and 300 patients who used an insulin pen.

The study found that patients whose doctors recommended the pen were far more likely to use pens than those whose doctors did not make such a recommendation. Other factors included having pens presented as an option, viewing pens as an aid to diabetes self-care, and believing that pens are not costly.

The advantages are many

Jane Seley, GNP, MPH, MSN, CDE, agrees that insulin pens are less popular in the United States primarily because most healthcare professionals are unfamiliar with them. In a November 2005 article for Diabetes Health (“Is an Insulin Pen Right for You?”), Seley wrote about the advantages of using an insulin pen. The pens, she said, are disposable, freeing you from the need to replace the insulin cartridge. They are small and easy to use, making it simpler to inject discreetly in a restaurant or other public place.

Furthermore, insulin cartridges hold only 300 units of insulin, whereas a vial holds 1,000 units. Because insulin should be discarded 28 days after being opened (except for pre-mixed insulin, which is good for only 10 to 14 days), often a vial must be tossed before all 1,000 units have been used. With a pen and a 300-unit cartridge, there is less chance that you will be wasting insulin. Finally, it is much easier to see the numbers on an insulin pen than on a syringe, making dosage errors less likely.

Do pens really cost more?

In a study funded by Novo Nordisk, researchers at Ohio State University found that people with type 2 diabetes who move from oral medications to insulin would be wise to start with an insulin pen rather than a syringe. It’s not because the pens cost less than syringes and vials; in fact, they cost more. Rather, it’s because type 2s who start their insulin with pens end up requiring less medical care.

The researchers compared 1,162 type 2 Medicaid patients who began insulin therapy with syringes to another 168 patients who began by using Novo Nordisk insulin pens. They found that only about half of the people in either group took their insulin properly, a sad fact that they attributed to the poor overall care that low-income people receive from Medicaid. Still, after summing up the costs of each group’s emergency room visits, hospitalizations, and outpatient visits for diabetes-related conditions, the average annual cost for syringe users was a whopping $31,764. For pen users, it was only $14,857.

In another study, the same researchers compared more than 1,100 patients who were already on insulin when the study began. Half switched to a pen, and half stayed on injections. In that study, the annual healthcare costs for pen users were slightly higher than those of  syringe users: $11,476 versus $10,755. The researchers explained this contradictory finding by noting that pens are more expensive initially. They also hypothesized that perhaps pen users took their insulin as often as they were supposed to and that syringe users didn’t, resulting in higher insulin costs for the pen users.

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“Factors affecting use of insulin pens by patients with type 2 diabetes”, by R. R. Rubin and M. Peyrot. Diabetes Care. November 26, 2007

American Diabetes Association


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