Insulin is a hormone that is vital for regulating blood sugar levels. It is used to treat diabetes, a condition where the body does not produce enough insulin or cannot properly utilize it. For people with diabetes who require insulin, knowing how to properly dose and administer insulin is extremely important for managing their condition.
What is Insulin?
Insulin is a peptide hormone that is produced by the beta cells in the pancreas. It helps regulate the metabolism of carbohydrates, fats, and proteins by promoting the absorption of glucose from the blood into liver, fat, and skeletal muscle cells. Insulin forces body cells to take in glucose from the blood and store it as glycogen. It also inhibits the breakdown of glycogen, fat, and protein. Therefore, insulin lowers blood sugar levels and prevents hyperglycemia (high blood sugar).
In healthy individuals, insulin is secreted at a constant, low level throughout the day. This basal insulin helps maintain normal blood sugar levels by balancing glucose production in the liver and glucose uptake in muscles and fat tissue. However, when blood sugar levels rise after eating, the pancreas secretes a spike of insulin to facilitate the uptake and utilization of the glucose by cells.
People with diabetes either do not produce enough insulin (type 1 diabetes) or are resistant to the effects of insulin (type 2 diabetes). This results in chronic high blood sugar levels. To manage their blood sugar, people with diabetes need to take supplemental insulin.
Types of Insulin
There are several types of insulin used to treat diabetes:
- Rapid-acting insulin – Starts working within 15 minutes, peaks in about 1 hour, and lasts 2 to 4 hours in the body. Examples are insulin lispro (Humalog), insulin aspart (Novolog), and insulin glulisine (Apidra).
- Regular or short-acting insulin – Starts working in 30 minutes to 1 hour, peaks in 2 to 3 hours, and lasts about 3 to 6 hours in the body. Example is human insulin (Humulin R).
- Intermediate-acting insulin – Starts working in 1 to 2 hours, peaks in 4 to 12 hours, and lasts approximately 12 to 18 hours. Examples include human insulin NPH (Humulin N) and insulin isophane (Novolin N).
- Long-acting insulin – Starts working several hours after injection, does not peak, and lasts approximately 20 to 26 hours. Examples are insulin detemir (Levemir) and insulin glargine (Lantus).
- Ultra long-acting insulin – Starts working 6 hours after injection, does not peak, and lasts beyond 24 hours. Example is insulin degludec (Tresiba).
- Pre-mixed insulin – Contains a fixed combination of a rapid or short-acting insulin with an intermediate or long-acting insulin in one vial. Examples are insulin lispro protamine suspension (Humalog Mix) and insulin aspart protamine suspension (Novolog Mix).
Rapid-acting insulin is usually taken at mealtimes to control the glucose spike after eating. Long-acting or intermediate-acting insulin is taken once or twice per day to provide basal insulin needs. People with type 1 diabetes require both basal and prandial (mealtime) insulin.
How is Insulin Administered?
Insulin can be administered through multiple routes:
- Subcutaneous injections – Insulin injections into the fatty tissue under the skin are the most common method of administration. This can be done using syringes, insulin pens, or insulin pumps.
- Intravenous infusion – Insulin can be given intravenously in a hospital setting for tighter blood glucose control.
- Inhaled insulin – Inhaled insulin was available for some time but has been discontinued. It allowed rapid absorption similar to subcutaneous insulin.
- Oral insulin – This is currently under development. Oral insulin would be convenient but is difficult to formulate because insulin is broken down in the GI tract before absorption.
- Transdermal patch – Patches with insulin to allow absorption through the skin are also being researched.
Subcutaneous injection into the abdomen, thighs, or upper arms is the predominant method for insulin administration. Insulin pens and pumps use short, small gauge needles for comfortable and convenient insulin delivery. Needle length is important to ensure the insulin is injected into the subcutaneous fat rather than the muscle.
Insulin Concentrations
Insulin comes in different concentrations or strengths. In the United States, insulin concentrations are expressed as units of insulin per milliliter (mL). Some common insulin concentrations are:
- U-100 – 100 units of insulin per mL
- U-200 – 200 units of insulin per mL
- U-300 – 300 units of insulin per mL
- U-500 – 500 units of insulin per mL
The higher concentration insulins, like U-500, allow delivery of higher doses of insulin in a smaller volume. They are typically used in patients with severe insulin resistance who require very high daily doses of insulin.
Most insulin preparations are U-100. A U-100 insulin contains 100 units of insulin in each milliliter. Some newer analog insulins are also available at U-200 concentration.
How Many Units are in 1 mL of Insulin?
For U-100 insulin, which is the standard concentration:
There are 100 units in 1 mL of U-100 insulin
Some examples:
- 1 mL of Humalog (U-100 insulin lispro) contains 100 units of insulin lispro
- 1 mL of Lantus (U-100 insulin glargine) contains 100 units of insulin glargine
- 1 mL of Novolin R (U-100 human regular insulin) contains 100 units of human regular insulin
For other insulin concentrations:
There are 200 units in 1 mL of U-200 insulin
There are 300 units in 1 mL of U-300 insulin
There are 500 units in 1 mL of U-500 insulin
So the number of units in 1 mL corresponds to the concentration of the insulin.
Measuring and Dosing Insulin
Insulin doses are prescribed and administered in units. Most syringes for injecting insulin have unit markings down the side so you can draw up the correct dose. Insulin pens also allow you to dial and deliver a specific number of units.
To draw up the right insulin dose using a syringe:
- Check the insulin concentration. If it is U-100 insulin, then 1 mL will contain 100 units.
- Draw air into the syringe equal to the dose you need to take. For example, draw 30 units of air for a 30 unit dose.
- Inject the air into the insulin vial. This equalizes the pressure in the vial.
- Turn the vial upside down and slowly withdraw the prescribed insulin dose. Align the plunger with the correct unit marking for your dose.
- Tap the barrel to move any air bubbles to the top and push them out before injecting.
- Inject the insulin subcutaneously based on your healthcare provider’s instructions.
For U-100 insulin, if your prescribed dose is:
- 10 units – Draw up 0.1 mL
- 15 units – Draw up 0.15 mL
- 20 units – Draw up 0.2 mL
And so on, with 100 units being 1 mL.
Here is a table summarizing the units of different volumes of U-100 insulin:
| Volume of U-100 Insulin | Units of Insulin |
|---|---|
| 0.1 mL | 10 units |
| 0.2 mL | 20 units |
| 0.5 mL | 50 units |
| 1 mL | 100 units |
For Insulin pens:
- Priming or dialing in 2 units on a pen will deliver 0.02 mL of U-100 insulin
- Priming or dialing in 5 units on a pen will deliver 0.05 mL of U-100 insulin
And so on, up to dialing in 100 units delivering 1 mL.
Key Takeaways
- For U-100 insulins, which are standard, there are 100 units in each milliliter (mL).
- 1 mL of a U-100 insulin formulation contains 100 units of insulin.
- The concentration of an insulin determines how many units there are per mL. Only U-100 has 100 units per mL.
- Always check the insulin concentration before administering it. This determines how much volume you need to draw up based on the prescribed units.
- With U-100 insulin, you can directly convert units to mL. 10 units = 0.1 mL, 20 units = 0.2 mL, and so on.
Frequently Asked Questions
How do I calculate the units in an insulin dose?
First check the concentration of the insulin. For U-100 insulin, each milliliter (mL) contains 100 units. So to calculate units:
- If taking 0.1 mL, multiply 0.1 * 100 = 10 units
- If taking 0.2 mL, multiply 0.2 * 100 = 20 units
- If taking 0.5 mL, multiply 0.5 * 100 = 50 units
Should insulin be kept refrigerated?
Yes, insulin should be refrigerated to maintain its potency. Unopened insulin can be kept refrigerated until the expiration date printed on the package. Once in use, it can be kept at room temperature for 28-56 days depending on the type of insulin. But refrigeration is best.
How long does insulin last after opening?
The timeframe depends on the type of insulin:
- Opened vials of rapid or short acting insulin (like Humalog or Novolin R) last 28 days.
- Opened vials of NPH (isophane) insulin (like Humulin N) last 28 days.
- Longer acting insulins like Lantus and Levemir last 56 days after opening.
Check packaging for specific information on each insulin type. Discard opened insulin after 28 or 56 days.
How long does an insulin pen or in-use insulin pump fill last?
The same general timeframes apply. An in-use insulin pen or pump reservoir should be discarded and replaced after:
- 28 days if using rapid or short acting insulin
- 56 days if using long acting insulin like Lantus or Levemir
However, always refer to storage guidelines for your specific insulin and delivery device.
Can I mix two types of insulin in one syringe?
You should not mix two insulins together unless it is a premixed combination like Humalog Mix 75/25. The mixes of rapid or short acting with intermediate or long acting insulin are pharmacologically formulated for use together. Mixing random insulins could alter their absorption and duration of action.
Conclusion
Understanding how many units of insulin are in each milliliter is very important for accurately dosing and administering insulin. For the commonly used U-100 insulin, there are 100 units in every 1 mL. So make sure to check the insulin concentration before drawing up doses. This allows you to precisely tailor the volume to the prescribed units and safely manage blood glucose levels.
