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, and where the insulin has been injected.

Insulin strength is usually U-100, or 100 units of insulin in one milliliter of fluid. Short-acting (regular) insulin is also available in U-500, or 500 units of insulin in one milliliter of fluid. This is five times more concentrated than U-100 regular insulin.

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. The insulin Humalog is a quick-acting insulin with a short length (duration) of action.

Rapid- and short-acting types of insulin take effect and wear off more quickly than long-acting insulins. The liquid insulins are clear and do not settle out when the bottle (vial) sits for a while. Rapid-acting insulin acts most like insulin 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 before dinner instead of a short-acting insulin, it may prevent severe drops in the blood sugar level in the middle of the night.

Intermediate- and long-acting types of insulin contain added substances (buffers) that make them work over a long time and may appear 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 (Lantus) and insulin detemir (Levemir) 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:

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