Insulin

Insulin

Patients with type 1 diabetes require an external source of insulin to control blood glucose levels. Insulin may also be given to pa-tients with type 2 diabetes.

Types of insulin include:

·                 rapid-acting: lispro

·                 short-acting: regular

·                 intermediate-acting: NPH

·                 long-acting: Ultralente.

Pharmacokinetics (how drugs circulate)

Insulin isn’t effective when taken orally because the GI tract breaks down the protein molecule before it reaches the blood-stream.

Under the skin

All insulins, however, may be given by subcutaneous (subQ) injec-tion. Absorption of subQ insulin varies according to the injection site, the blood supply, and degree of tissue hypertrophy at the in-jection site.

In the I.V. league

Regular insulin may also be given by I.V. infusion as well as in dialysate fluid infused into the peritoneal cavity for patients on peritoneal dialysis therapy.

Distribution, metabolism, and excretion

After absorption into the bloodstream, insulin is distributed throughout the body. Insulin-responsive tissues are located in the liver, adipose tissue, and muscle. Insulin is metabolized primarily in the liver and to a lesser extent in the kidneys and muscle, and it’s excreted in stool and urine.

Pharmacodynamics (how drugs act)

Insulin is an anabolic, or building, hormone that helps:

·                 promote storage of glucose as glycogen

·                 increase protein and fat synthesis

·                 slow the breakdown of glycogen, protein, and fat

·                 balance fluids and electrolytes

Insulin’s special effects

Although it has no antidiuretic effect, insulin can correct the poly-uria (excessive urination) and polydipsia (excessive thirst) associ-ated with the osmotic diuresis that occurs in hyperglycemia by de-creasing the blood glucose level. Insulin also facilitates the move-ment of potassium from the extracellular fluid into the cell. (See How insulin aids glucose uptake.)

Pharmacotherapeutics (how drugs are used)

Insulin is indicated for:

·                 type 1 diabetes

·                 type 2 diabetes when other methods of controlling blood glu-cose levels have failed or are contraindicated

·                 type 2 diabetes when blood glucose levels are elevated during periods of emotional or physical stress (such as infection and surgery)

·                 type 2 diabetes when oral antidiabetic drugs are contraindicated because of pregnancy or hypersensitivity

·                 gestational diabetes.

When things get complicated

Insulin is also used to treat two complications of diabetes: diabet-ic ketoacidosis, more common with type 1 diabetes, and hyperos-molar hyperglycemic nonketotic syndrome, which is more com-mon with type 2 diabetes.

What? But I don’t have diabetes…

Insulin is also used to treat severe hyperkalemia (elevated serum potassium levels) in patients without diabetes. Potassium moves with glucose from the bloodstream into the cell, lowering serum potassium levels.

Drug interactions

Some drugs interact with insulin, altering its ability to decrease the blood glucose level; other drugs directly affect glucose levels:

·                 Anabolic steroids, salicylates, alcohol, and monoamine oxidase inhibitors (MAOIs) may increase the hypoglycemic effect of in-sulin.

·                 Corticosteroids, sympathomimetic drugs, thiazide diuretics, and dextrothyroxine sodium may reduce the effects of insulin, result-ing in hyperglycemia.

·                 Beta-adrenergic blockers may prolong the hypoglycemic effect of insulin and may mask signs and symptoms of hypoglycemia. (See Adverse reactions to insulin.)