Insulin is used as injections in the treatment of insulin deficiency states (type 1 diabetes) and relative insulin deficiencies (type 2 diabetes). Insulin preparations are of several varieties and the types depend on how quickly they work, when they peak, and how long their actions last.

Insulin is available in different strengths; the most common is U-100. All the insulin in use is manufactured in a laboratory, but animal insulin is still being used in some parts of the world.

Animal insulin

Pig (porcine) insulin and cow (bovine) insulin are very similar to human insulin. For many years, the insulin used by people with diabetes was produced from the pancreases of these animals.

Synthetic human insulin derived from genetically engineered bacteria first became available in the 1980s and has now replaced all available insulin.

What is biosynthetic insulin?

Normally insulin is produced in the pancreas where the beta cells make the hormone insulin. With each meal, beta cells release insulin to help the body use or store the blood glucose it gets from food. In people with type 1 diabetes, the pancreas no longer makes insulin. Due to auto-immune mechanism, some individuals develop an immune reaction to their beta cells that kills the insulin producing cells. These individuals need insulin shots to use glucose from meals.

Insulin cannot be taken as a pill because it would be broken down during digestion just like the protein in food. It must be injected into the fat just under the skin to be utilized.

Insulin is synthesized in the laboratories using bacterial cells that have been genetically modified to produce human insulin. This is called Recombinant DNA technology.

Characteristics of Insulin

Insulin preparations are characterized by three cardinal features:

• Onset of action – length of time before insulin reaches the bloodstream and begins lowering blood glucose.
• Peak of action – The time during which insulin is at maximum effectiveness in terms of lowering blood glucose.
• Duration – the length of time the insulin continues to lower blood glucose

Types of Insulin

There are several varieties of biosynthetic insulin in use. Some of these are:

1. Rapid-acting insulin – These include insulin lispro (Eli Lilly), insulin aspart (Novo Nordisk), or insulin glulisine (sanofi-aventis). They start to work in around 5 minutes after injection and the action peaks at about 1 hour, and continues to work for 2 to 4 hours.
2. Regular or Short-acting insulin (human) or Soluble insulin – This takes around 30 minutes to act and peaks at 2 to 3 hours after injection, and is effective for approximately 3 to 6 hours. This type of insulin may also be injected into the veins (intravenous insulin).
3. Intermediate-acting insulin (human) – This insulin takes around 2 to 4 hours to act and peaks 4 to 12 hours later, and is effective for about 12 to 18 hours.
4. Long-acting insulin (ultralente) – this type of insulin begins to act in 6 to 10 hours after injection and is usually effective for 20 to 24 hours. There are also two long-acting insulin analogues: glargine and detemir. They both tend to lower glucose levels fairly evenly over a 24-hour period with less of a peak of action than ultralente.
5. Premixed insulin – This is insulin with a combination of above types in a single insulin vial. They usually contain pre-mixed combinations of either a rapid onset-fast acting or a short acting insulin and intermediate acting insulin. This can help people who have trouble drawing up insulin out of two bottles and reading the correct directions and dosages. These are cloudy in appearance.

Insulin Strength

Insulins are supplied in vials as dissolved or suspended liquids. However, the solutions have different strengths. The most commonly used strength in the United States today is U-100, which means it has 100 units of insulin per milliliter of fluid. Other units include U40, which has 40 units of insulin per milliliter of fluid that is used in Europe and in Latin America.

Insulin Additives

Biosynthetic insulin preparations have added ingredients. These prevent bacteria from growing and help maintain a neutral balance between acids and bases. In some rare cases, the additives can bring on an allergic reaction.

How is insulin given?

There are many different devices available to inject insulin. These include:

• Injections – these are the most common route of insulin use. Insulin syringes are to be used with insulin vials (10 ml).
• Insulin delivery devices - devices are available in different shapes and sizes. There may be insulin cartridge (3ml, containing 300 units of insulin) that fits into a device. When finished, a new cartridge is inserted. There may be pen devices are pre-filled with insulin.