Three Basic Categories of Insulin and How it Relates to You

Insulin is a complex, large-protein molecule produced by spe­cialized "beta" cells in the islets of Langerhans in the pan­creas. The pancreas, of course, serves many purposes in addition to secreting insulin. It's a complex organ and plays a crucial role in secretion of digestive enzymes used in the breakdown of food.

The following information briefly explains the importance of insulin. This is only a basic guide. Insulin is manufactured, stored, and secreted directly into the bloodstream by the beta cells in the pancreas. Insulin plays a vital role in breaking food down into the various com­ponents needed to produce energy and sustain life.

This complex metabolic process allows our bodies to con­tinually make and repair cells and tissues, even when we haven't eaten for a while. Insulin is a key component needed to move glucose into the body's cells for energy and to control how much glucose is in the blood.

Specifically, insulin inhibits a process called glycogenolysis (the breakdown of animal starch) and gluconeogenesis (the formation of new glucose from protein). In this way the blood glucose is lowered through an alternate pathway.

Understanding insulin and its actions within the human body is crucial to understanding diabetes.

There are three basic categories of insulin: short-acting, inter­mediate-acting, and long-acting. Each is distinguished by its onset of action, peak, and duration. Onset means the time it takes the insulin to begin exerting its effect. Peak is the time insulin is working its hardest to lower blood glucose. And duration refers to how long it lasts.

The most recent development in this area is a new form of short-acting insulin: lispro. This insulin analog (a close mole­cular cousin to insulin) is sold under the brand name of Humalog. It starts working within minutes, permitting diabetics to eat right after injection.

Action times vary greatly from person to person, and between animal insulin and human insulin.

Lispro has its onset within 5 minutes and peaks in one hour. Its usual dura­tion is two to four hours. Regular has its onset within 30 to 60 minutes and peaks in two to four hours. Its duration is four to six hours. This insulin is clear and requires no rolling action to ensure proper mixing within the vial. Regular insulin tra­ditionally has been used in conjunction with other insulin types. Today, it is popular to use regular insulin alone in four to six injections spread over a 24-hour period.

Generally, proper injection time of Regular insulin is 30 to 60 minutes before meals. With lispro, you can start eating almost immediately. (The manufacturer recommends eating within 15 minutes after injection.) This allows an onset inter­val before the insulin acts. Onset will then coincide with the ingestion of your meal, making the action of the insulin as close to normal as possible.

Intermediate-acting insulin, known as NPH or Lente, begins to work in 60 to 90 minutes. Peak action is at 8 to 12 hours, with duration of up to 24 hours. This insulin type is cloudy, and the vial must be carefully rolled in the palms of the hands to ensure good mixing. Never shake this type of insulin to mix it. Insulin is a delicate protein and should never be vigorously agitated. Shaking also produces frothing or bub­bles that make it more difficult to withdraw.

Long-acting insulin, known as Ultralente, has its onset at 6 to 10 hours, peaks in 12 to 18 hours, and has a duration of 20 to 30 or more hours. Ultralente supplies a basal level of insulin and must be used with multiple doses of regular insulin. This insulin also is cloudy, and the vial should always be carefully rolled in the palms of the hands to ensure proper mixing.

A single vial preparation of premixed insulin, made up of regular insulin and NPH intermediate-acting insulin, is typi­cally available in a 70:30 ratio-70 parts of NPH intermediate to 30 parts of regular short-acting insulin. If you were to take 30 units of this insulin, using the 70:30 ratio, you would be taking 9 units of regular insulin with 21 units of NPH. Pre­mixed insulin is also now available in a 50:50 ratio.

I recommend carefully weighing the convenience of the' single vial approach against the versatility of mixing regular and NPH insulin in separate vials. The premixed preparation is difficult for the beginner and sometimes even for the vet­eran diabetic to work with. By all means, check with your doctor and be sure you understand this insulin well before you and your doctor agree to use it. The premixed insulin is cloudy because it contains NPH. The same care is needed as with other cloudy-appearing insulins.

Remember, regular insulin is always clear. If it appears slightly cloudy, don't use it. How does a blind person know which insulin is which? Take a close look at the shapes of the various vials of insulin. They are shaped differently to help you make sure you're taking the right amount and the right type of insulin.