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[L. insula, island + -in]
A hormone secreted by the beta cells of the pancreas. As a drug, insulin is used principally to control diabetes mellitus. Insulin therapy is required in the management of type 1 diabetes mellitus because patients with this illness do not make enough insulin on their own to survive. The drug is also used in the care of patients with gestational diabetes to prevent fetal complications caused by maternal hyperglycemia (insulin itself does not cross the placenta or enter breast milk). In type 2 diabetes mellitus, insulin is typically reserved for those patients who have failed to control their blood sugars with diet, exercise, and oral drugs.
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Insulin preparations differ with respect to the speed with which they act and their duration and potency following subcutaneous injection. SEE TABLE: Duration of Effect of Various Insulins When Given by Subcutaneous Injection*

In the past, insulin for injection was obtained from beef or swine pancreas. These peptides differed from human insulin by a few amino acids, causing some immune reactions and drug resistance. Most insulin now in use is made by recombinant DNA technology and from an immunological perspective is equivalent to human insulin.

In health, the pancreas secretes insulin in response to elevations of blood glucose, such as occur after meals. It stimulates cells, esp. in muscular tissue, to take up sugar from the bloodstream. It also facilitates the storage of excess glucose as glycogen in the liver and prevents the breakdown of stored fats. In type 1 diabetes mellitus, failure of the beta cells to produce insulin results in hyperglycemia and ketoacidosis.

The insulin dosage should always be expressed in units. There is no average dose of insulin for diabetics; each patient must be assessed and treated individually Doses are titrated gradually to achieve near normal glucose levels, about 90 to 125 mg/dL.

The FDA requires that all preparations of insulin contain instructions to keep in a cold place and to avoid freezing.

Descriptive text is not available for this imageThose who use insulin should wear an easily seen bracelet or necklace stating that they have diabetes and take insulin. This helps ensure that patients with hypoglycemic reactions will be diagnosed and treated promptly.

Duration of Effect of Various Insulins When Given by Subcutaneous Injection*
Type of InsulinGeneric (Trade Names)Onset (hr)Maximum (hr)Duration (hr)
Very rapidAspart (NovoLog)0.2-0.51-33-5
Very rapidLispro (Humalog)0.2-0.50.5-2.53-5
Very rapidGlulisine (Apidra)0.2-0.51.6-2.83-4
Intermediate-actingNPH (Humulin N, Novolin N)2-44-1210-18
Fixed-dose combination insulins †70/30, 50/50, etc.Variable, depending on mixture used
Very long- actingGlargine (Lantus)2-4none11-32
Very long- actingDetermir (Levemir)3-43-96-23 Dose dependent
U 500 regular very concentrated (5 X U100)0.5-1.02.5-5up to 24 hr

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