What is insulin?
Insulin is a hormone produced and released by beta cells in the pancreas. Insulin is released to help the body to regulate blood glucose. Insulin release is triggered by an increase in blood glucose from food consumption.
When is insulin used?
Insulin is used in the treatment of both diabetes mellitus (DM) type 1 and type 2. In type 1 diabetes, the pancreas no longer can produce insulin because the beta cells are destroyed. Therefore, all type 1 diabetes patients must receive insulin to regulate their blood glucose. In type 2 diabetes there still is some insulin being produced but the body does not respond well to it. In this case a patient can start with medications that help increase insulin sensitivity. In later stages of diabetes if other medications are not effective a patient may start insulin to help the body regulate blood glucose.
Different types of insulin
There are several different types of insulin. There are advantages and disadvantages to each type of insulin and there is no clear "go to" insulin. Each insulin is classified based on its onset, peak, and duration of action.
- The onset of action means the time it takes for the insulin to start working to lower blood glucose.
- The peak is the time when the insulin produces its maximum effect on blood glucose.
- The duration of action is the total amount of time the insulin will be effective in lowering blood glucose.
Side effects associated with all types of insulin include hypoglycemia (low blood sugar), weight gain, allergic reactions, hypokalemia (low potassium), and injection site reactions such as rash or pruritus (itching).
The four different types of insulin used in the treatment of diabetes are rapid-acting, short-acting, immediate-acting, and long-acting. Regardless of which type of insulin is used, patients should be monitored in the first few weeks of starting insulin and throughout treatment to ensure the dosage is appropriate. Each patient will respond to insulin differently and will need adjustments based on blood glucose readings to achieve target HbA1c goals and minimize hypoglycemic episodes.
Rapid-acting insulin: This type of insulin is administered just before a meal to help control blood glucose that will come from the meal. Since this insulin works very quickly it is convenient for patients to just inject and eat. The patient does not need to plan in advance when to eat. Rapid-acting insulin is also more effective at lowering postprandial (after meals) blood glucose than regular insulin. A disadvantage with this type of insulin is that the patient will have to inject at least two to three times a day to compensate for each meal. In addition, it is usually used along with an intermediate or long acting insulin.
Humalog (insulin lispro)- Onset: 15-30 minutes, Peak: 1-2 hours, Duration: 3-4 hours
Novolog (insulin aspart)- Onset: 15-30 minutes, Peak: 1-2 hours, Duration: 3-5 hours
Apidra (insulin glulisine)- Onset: 15-30 minutes, Peak: 1-2 hours, Duration: 3-4 hours
Regular or Short-acting insulin: Similar to rapid-acting insulin, this regular or short-acting insulin is also administered before a meal to help control blood glucose that will come from the meal. Since regular insulin takes slightly longer to start working patients will have to inject about 30 minutes before eating. This requires more planning and coordination of insulin injections around meal times. On the other hand effect of regular insulin will last longer than rapid-acting insulin and will reduce blood glucose for a longer period of time. Regular insulin's slower onset does not hold true when administered intravenously (IV) and is used in hospitals to reduce blood glucose quickly.
Humulin R (regular)- Onset: 30-60 minutes, Peak: 2-3 hours, Duration: 4-6 hours
Novolin R (regular)- Onset: 30-60 minutes, Peak: 2-3 hours, Duration: 4-6 hours
Intermediate-acting (NPH): This type of insulin is usually used along with rapid or short acting insulin to maintain blood glucose when rapid or short acting insulin wears off. Intermediate acting insulins are usually injected twice a day. A disadvantage with using this type of insulin is that the patient must roll the vial to mix the contents before injecting.
Humulin N - Onset: 2-4 hours, Peak: 4-8 hours, Duration: 8-12 hours
Novolin N - Onset: 2-4 hours, Peak: 4-8 hours, Duration: 8-12 hours
Long-acting insulin: This type of insulin is usually used long with rapid or short acting insulin to help maintain blood glucose after rapid or short acting insulin wears off. Long-acting insulin does not have a peak which means that its effects stays constant throughout the day. Type 2 diabetes patients are usually started on this type of insulin. Long-acting insulin alone is usually not sufficient to achieve blood glucose goals. Addition of a rapid or short acting insulin is usually needed. Lantus is injected once at bedtime while Levemir is injected once or twice (divided doses) daily. There is a slight structural difference in molecular structure of the two insulins. In contrast to Lantus, Levemir has a fatty acid attached at the B-29 amino acid position and the B-30 amino acid is removed.
Lantus (insulin glargine) Solostar Pen - Onset: 4-5 hours, Peak: no peak, Duration: 22-24 hours
Levemir (insulin detemir) Flex Pen - Onset: 2 hours, Peak: no peak, Duration: 14-24 hours
Premix Insulin : This type of insulin is mixed with the combination of a rapid or short acting insulin and an intermediate acting insulin. Long-acting insulin should never be mixed with any other type of insulin. The premix insulin allows less injections because patients will receive rapid or short acting insulin to cover meals while the intermediate acting insulin will act between meals as mentioned above. This can be more convenient for patients who would like to minimize the amount of injections. Below are some of the premix insulin available.
Humalog Mix 75/25 (75% NPH, 25% lispro)
Novolog Mix 70/30 (70% NPH, 30% aspart)
Humalog Mix 50/50 (50% NPH, 50% lispro)
Humulin 70/30 (70% NPH, 30% regular)
Novolin 70/30 (70%NPH, 30% regular)
Inhaled Insuin: Afrezza is a newly approved man-made insulin that is available as an inhalation powder. Upon inhalation, the insulin powder is quickly absorbed from the lungs into the blood stream. Like other insulins, Afrezza regulates blood glucose (sugar) by reducing the amount of glucose produced by the liver, as well as increasing uptake of glucose by cells. Learn more about Afrezza.
Herbst, K. L., and I. B. Hirsch. "Insulin Strategies for Primary Care Providers."Clinical Diabetes 20.1 (2002): 11-17. Web. 27 May 2014.
Barag, Steven H., DO. "JAOA - The Journal of the American Osteopathic Association." Insulin Therapy for Management of Type 2 Diabetes Mellitus: Strategies for Initiation and Long-term Patient Adherence. N.p., n.d. Web. 27 May 2014.
Dipiro, Joseph T. "Chapter 83 Diabetes Mellitus." Pharmacotherapy. a Pathophysiologic Approach. New York: McGraw-Hill Education, 2014. N. pag. Print.