Insulin
Insulin
Patients with type 1 diabetes require an external source of insulin to control blood glucose levels. Insulin may also be given to patients 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 bloodstream.
Under the skin
All insulins, however, may be given by subcutaneous (subQ) injection. Absorption of subQ insulin varies according to the injection site, the blood supply, and degree of tissue hypertrophy at the injection 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.
How insulin aids glucose uptake
These illustrations show how insulin allows a cell to use glucose for energy.
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) associated with the osmotic diuresis that occurs in hyperglycemia by decreasing the blood glucose level. Insulin also facilitates the movement of potassium from the extracellular fluid into the cell.
Pharmacotherapeutics (how drugs are used)
Insulin is indicated for:
- type 1 diabetes
- type 2 diabetes when other methods of controlling blood glucose 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: diabetic ketoacidosis, more common with type 1 diabetes, and hyperosmolar hyperglycemic nonketotic syndrome, which is more common 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 insulin.
- Corticosteroids, sympathomimetic drugs, thiazide diuretics, and dextrothyroxine sodium may reduce the effects of insulin, resulting 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.)
Adverse reactions to insulin
Adverse reactions to insulin include:
- hypoglycemia (below-normal blood glucose levels)
- Somogyi effect (hypoglycemia followed by rebound hyperglycemia)
- hypersensitivity reactions
- lipodystrophy (disturbance in fat deposition)
- insulin resistance.
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