The food we eat is converted into glucose which is used for energy by the cells of the body. Insulin is a protein produced by the pancreas that allows glucose to enter the cells. Insulin was discovered in 1921 by a team of Canadian scientists. Before the discovery of insulin, diabetes was a fatal disease.

The first insulins used were extracted from beef and pig pancreas. Insulin normally acts quickly and is removed from the body rapidly. Changes were made to insulin to make it longer acting to reduce the number of injections required throughout the day. These insulins were called NPH, lente, semilente, and ultralente. These products were used to treat diabetes through the 1980's when human insulin was synthesized. Now human forms of insulin are used almost exclusively to treat diabetes. A variety of types of human insulin have been introduced to allow greater flexibility, convenience, and improved response with insulin treatment.

Different terms are used to describe the actions of insulin. Onset describes how soon it starts to lower glucose after it is injected. Peak is the time to maximum effect. Duration is how long the effect lasts. Different insulins are differentiated by changes in these effects.

Rapid-acting insulins have an onset of 15 minutes, peak in 30 to 90 minutes and duration of 3 to 5 hours. These include Humalog, Novolog, and Apidra.

Short-acting insulins have an onset of 30 to 60 minutes, peak in 2 to 4 hours, and last 5 to 8 hours. These include Humulin R and Novolin R and are known as regular insulins.

Intermediate-acting insulins have an onset of 1 to 3 hours, peak in 8 hours and last 12 to 16 hours. These include Humulin N and Novolin N and are known as NPH insulins.

Long-acting insulins have an onset of 1 hour, do not peak but provide a steady effect over a duration of 20 to 26 hours. These include Levemir and Lantus and are known as basal insulins.

By combining different types of insulin, diabetic patients today can much better control their blood glucose levels, which can greatly reduce the risk of serious complications of diabetes. Some combinations are commercially available pre-mixed to provide rapid onset and longer duration of action with a single injection.

References: http://diabetes.niddk.nih.gov/dm/pubs/medicines_ez/insert_C.htm, http://content.karger.com/ProdukteDB/Katalogteile/isbn3_8055/_83/_53/Insulin_02.pdf.

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