Types of Insulin Therapy
Insulin is a hormone that is produced by the pancreas. It is needed for the body to make and store energy from food. Without insulin, the muscle, fat and liver cells are not able to use glucose to make energy or metabolize proteins or fats. Diabetes mellitus is a condition in which the body either does not produce or does not use insulin correctly. All type 1 diabetics, and some type 2 diabetics, require insulin therapy to treat the disease.
Several types of insulin are available and are grouped according to how fast they work: rapid-acting, short-acting, intermediate-acting and long-acting.
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Availability of Insulin
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Insulin is commercially available in human, pork and beef-pork insulin analogs. Most formulations are available in a concentration of 100 insulin units per 1 milliliter. Some insulin is available in concentrations of 500 units per 1 milliliter, but its use is reserved for cases of extreme insulin resistance and patients requiring excessive doses of insulin.
Variability of Insulin Therapy
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The action of any insulin depends on the type of insulin, dose, site of injection, blood supply, temperature and physical activity. Insulin therapy is variable and requires individualized dose adjustments and constant medical supervision.
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Rapid- and Short-Acting Insulins
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Rapid-acting insulin starts working within 15 to 30 minutes of injection, exhibits peak activity in one to two hours, and lasts three to four hours. Short-acting insulin, or regular insulin, starts working within 30 to 60 minutes, peaks two to four hours after administration, and lasts for five to seven hours. Both rapid- and short-acting insulins are taken with meals to mimic the body's natural production of an insulin bolus in response to the ingestion of food.
Intermediate-Acting Insulin
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Intermediate-acting insulin is known as NPH insulin and starts working within three hours of injection. The activity peaks at six hours, and lasts 10 to 12 hours. NPH insulin is usually injected twice daily to mimic the body's normal basal levels of insulin.
Long-Acting Insulin
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Long-acting insulin begins working within four hours, but the activity remains constant throughout the rest of the day--there is no peak in activity. Similar to intermediate-acting insulin, long-acting insulin mimics the basal level of insulin but is only administered once daily, typically in the evening.
Administration
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Most insulin is administered subcutaneously, through single-use syringes, insulin pumps or multiple-dose pre-filled pens. Regular insulin may be administered intravenously or intramuscularly for certain medical conditions, such as for those critically ill or for surgical patients.
Drug Interactions
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Some medications and foods alter the action of insulin and increase the risk for hypoglycemia. Patients using insulin therapy should avoid alcohol, MAOI inhibitors, beta blockers, and anabolic steroids. Patients with type 2 diabetes who are taking oral antidiabetic agents in addition to insulin are also at an increased risk for hypoglycemia.
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References
- DiPiro JP, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A pathophysiologic approach. 5th ed. New York, New York: McGraw-Hill; 2002.
- Lacy CF, Armstrong LL, Goldman MP, Lance LL. Drug information handbook. 11th ed. Hudson, OH: Lexi-Comp; 2003.
- Rhoades R, Pflanzer R. Human Physiology. 4th ed. Pacific Grove, CA: Thomason Learning; 2003.
