Topic Overview

Insulin is used to treat people who have diabetes. Each type of insulin acts over a specific amount of time. The amount of time can be affected by exercise, diet, illness, some medicines, stress, the dose, how you take it, or where you inject it.

Insulin strength is usually U-100 (or 100 units of insulin in one millilitre of fluid). Short-acting (regular) insulin is also available in U-500. This is five times more concentrated than U-100 regular insulin. Long-acting insulin (glargine) is also available in U-300. This is three times more concentrated than U-100 long-acting insulin. Be sure to check the concentration of your insulin so you take the right amount.

Insulin is made by different companies. Make sure you use the same type of insulin consistently.

Rapid-acting insulins work over a narrow, more predictable range of time. Because they work quickly, they are used most often at the start of a meal. Rapid-acting insulin acts most like insulin that is produced by the human pancreas. It quickly drops the blood sugar level and works for a short time. If a rapid-acting insulin is used instead of a short-acting insulin at the start of dinner, it may prevent severe drops in blood sugar level in the middle of the night.

Short-acting insulins take effect and wear off more quickly than long-acting insulins. A short-acting insulin is often used 30–60 minutes before a meal so that it has time to work. These liquid insulins are clear and do not settle out when the bottle (vial) sits for a while.

Intermediate- and long-acting insulins contain added substances (buffers) that make them work over a long time and that may make them look cloudy. When these types of insulin sit for even a few minutes, the buffered insulin settles to the bottom of the vial. But insulin glargine and insulin detemir are clear liquids (not cloudy).

Mixtures of insulin can sometimes be combined in the same syringe, for example, intermediate-acting and rapid- or short-acting insulin. Not all insulins can be mixed together.

For convenience, there are premixed rapid- and intermediate-acting insulin. The insulin will start to work as quickly as the fastest-acting insulin in the combination. It will peak when each type of insulin typically peaks, and it will last as long as the longest-acting insulin. Examples include:

• 30% regular and 70% NPH (Humulin 30/70, Novolin ge 30/70).
• 50% lispro and 50% lispro protamine (Humalog Mix 50).
• 25% lispro and 75% lispro protamine (Humalog Mix 25).
• 30% aspart and 70% aspart protamine (NovoMix 30).