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Insulin is available in different strengths; the most common is U-100.

All insulin available in the United States is manufactured in a laboratory, but animal insulin can still be imported for personal use.

Inside the pancreas, 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. The beta cells have been destroyed and they need insulin shots to use glucose from meals. People with type 2 diabetes make insulin, but their bodies don’t respond well to it. Some people with type 2 diabetes need diabetes pills or insulin shots to help their bodies use glucose for energy. 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 under your skin for it to get into your blood.

There are several types of insulin. They are:

Rapid-acting insulin, such as insulin lispro (Eli Lilly), insulin aspart (Novo Nordisk), or insulin glulisine (sanofi-aventis), begins to work about 5 minutes after injection, peaks in about 1 hour, and continues to work for 2 to 4 hours.

Regular or Short-acting insulin (human) usually reaches the bloodstream within 30 minutes after injection, peaks anywhere from 2 to 3 hours after injection, and is effective for approximately 3 to 6 hours.

Intermediate-acting insulin (human) generally reaches the bloodstream about 2 to 4 hours after injection, peaks 4 to 12 hours later, and is effective for about 12 to 18 hours.

Long-acting insulin (ultralente) reaches the bloodstream 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.

Premixed insulin can be helpful for people who have trouble drawing up insulin out of two bottles and reading the correct directions and dosages. It is also useful for those who have poor eyesight or dexterity and is convenient for people whose diabetes has been stabilized on this combination.

Insulin has 3 characteristics. They are:

Onset, which is the length of time before insulin reaches the bloodstream and begins lowering blood glucose.

Peaktime, which is the time during which insulin is at maximum strength in terms of lowering blood glucose.

Duration, which is how long insulin continues to lower blood glucose.

All insulins come dissolved or suspended in 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. U40, which has 40 units of insulin per milliliter of fluid, is not used in the U.S., but is still used in Europe and in Latin America. If you’re traveling outside of the U.S., be certain to match your insulin strength with the correct size syringe.

All insulins have added ingredients. These prevent bacteria from growing and help maintain a neutral balance between acids and bases. In addition, intermediate and long-acting insulins also contain ingredients that prolong their actions. In some rare cases, the additives can bring on an allergic reaction.

For many years, the insulin used by people with diabetes was produced from the pancreases of pigs and cows. Synthetic human insulin derived from genetically engineered bacteria first became available in the 1980s, and now all insulin available in the United States is manufactured in a laboratory. Although the development of synthetic human insulin was a boon for most people, especially those who were allergic to the animal insulins, a few people find that they can manage their diabetes better using animal insulins.

Although animal insulins are no longer produced in the United States, the FDA allows individuals to import animal insulins for their own personal use.