Insulin: Nursing Pharmacology Study Guide

Disease Spotlight: Diabetes Mellitus

Diabetes mellitus (literally "honey urine") is a complex disturbance in the metabolism of carbohydrates, proteins, and fats. It thickens the layer beneath the endothelial lining of the blood vessels, which narrows them, remodels them, and cuts blood flow. The most frequent signs are hyperglycemia and sugar in the urine (glycosuria). The American Diabetes Association diagnoses diabetes at a fasting plasma glucose of 126 mg/dL or higher (fasting plasma glucose of 100 to 125 mg/dL is prediabetes); other diagnostic routes are an A1C of 6.5% or higher, a 2-hour glucose tolerance test of 200 mg/dL or higher, or a random glucose of 200 mg/dL or higher with classic symptoms.

There are two types. Type 1 shows up in younger people and is linked to viral destruction of the pancreatic beta cells. Type 2 is adult-onset and comes from too little insulin to hold glucose control.

Hyperglycemia (high blood sugar) is a rise in blood glucose, with fatigue, lethargy, irritation, glycosuria, polyphagia, polydipsia, and itchy skin (from wastes the liver cannot clear). Hypoglycemia begins at a blood glucose of 70 mg/dL or below, the ADA level 1 alert value where you treat with fast-acting carbohydrate; readings under 54 mg/dL are clinically significant (level 2). It shows up in starvation, overtreatment of hyperglycemia, and other situations, bringing headache, paresthesias, hunger, and diaphoresis.

Therapeutic Action

Insulin replaces endogenous insulin, the only parenteral antidiabetic agent for that job. It reacts with cell receptors to move metabolites and ions across cell membranes and stimulates the synthesis of glycogen from glucose, fats from lipids, and proteins from amino acids.

Indications

• Treatment of type 1 diabetes
• Treatment of type 2 diabetes when other agents have failed
• Short-term treatment of type 2 diabetes during periods of stress
• Management of diabetic ketoacidosis, hyperkalemia, and marked insulin resistance

Pharmacokinetics

Here are the characteristic interactions of insulin and the body in terms of absorption, distribution, metabolism, and excretion:

Contraindications and Cautions

There are no true contraindications, since insulin is a replacement hormone, but pregnant and lactating women need close monitoring and dose adjustment. It is the drug of choice for managing diabetes in pregnancy. Insulin does enter breast milk, but the GI tract destroys it and it does not affect the nursing infant. Insulin-dependent mothers may make less milk because of insulin's effect on fat and protein metabolism.

Adverse Effects

Hypoglycemia and ketoacidosis, plus local reactions at the injection site (lipodystrophy).

Interactions

MAOIs, beta blockers, salicylates, and alcohol increase glucose reduction. Beta blockers carry a second danger: by blocking the SNS they mask many signs and symptoms of hypoglycemia, so the patient cannot tell it is happening. Several herbal therapies (juniper berries, ginseng, garlic, fenugreek, coriander, dandelion root, celery) raise the risk of hypoglycemia.

Nursing Considerations

Nursing Assessment

Screen for contraindications and cautions (allergy history, pregnancy) so you can set up the right monitoring and dose adjustments. Get a baseline physical exam. Assess skin lesions, orientation and reflexes, and blood pressure, pulse, respiration, and adventitious breath sounds, which can signal a response to high or low glucose and flag risks before you give insulin. Inspect the planned injection sites for bruising, thickening, or scarring that would slow absorption and skew the response. Draw blood glucose as ordered to track response, assess activity and exercise level (both shift serum glucose and drug need), and check urinalysis for glucosuria.

Nursing Diagnoses and Care Planning

• Risk for unstable blood glucose related to ineffective dosing of antidiabetic agents
• Imbalanced nutrition: less than body requirements related to the use of insulin and underlying disease process
• Risk for infection related to glucose levels

Nursing Implementation with Rationale

Confirm the patient has a diet and exercise plan and good hygiene to improve insulin effect and cut the complications of the disease, and monitor nutritional status for consults as needed. Gently roll the vial rather than shaking it hard to keep the suspension uniform. Rotate injection sites to spare the muscle and prevent subcutaneous atrophy. Always verify which insulin you are giving, because each has a different peak and duration and the names are easy to confuse. When mixing, give a regular and NPH mixture within 15 minutes of combining them to hold the right suspension and effect. Store insulin cool and out of direct sunlight; predrawn syringes stay stable for 1 week refrigerated. Track food intake, exercise, and activity to keep the effect on target and avoid hypoglycemia. Watch for sensory losses that affect safety and the patient's ability to draw up and inject the dose. Give good skin and foot care to head off serious infection, and provide comfort measures and teaching on drug effects and warning signs to report.

Evaluation

Track response to therapy (stable blood glucose) and watch for adverse effects (hypoglycemia, ketoacidosis, injection-site irritation). Confirm understanding by having the patient name the drug, its indication, and the adverse effects to watch for, and monitor compliance.

Frequently Asked Questions

At what blood glucose do you treat hypoglycemia? At 70 mg/dL or below. The ADA sets 70 mg/dL as the level 1 alert value, the point to treat with a fast-acting carbohydrate. A reading under 54 mg/dL is level 2, clinically significant whether or not the patient has symptoms.

How is diabetes diagnosed from a fasting glucose? A fasting plasma glucose of 126 mg/dL or higher meets the ADA threshold for diabetes. A fasting value of 100 to 125 mg/dL is prediabetes, and 70 to 99 mg/dL is normal.

Why do beta blockers make insulin more dangerous? They blunt the sympathetic response, so they mask the early warning signs of hypoglycemia such as tremor and tachycardia. The patient may not feel a low coming, which raises the risk of a severe drop.

Which insulin do you draw up first when mixing? Draw the clear (regular or rapid-acting) insulin before the cloudy (NPH), and give a regular and NPH mixture within about 15 minutes of combining them so the suspension holds. Roll the vial gently rather than shaking it.

Is insulin safe in pregnancy? Yes, it is the drug of choice for managing diabetes in pregnancy. It does pass into breast milk, but the infant's GI tract destroys it, so it does not affect the nursing baby.

How long do prefilled insulin syringes last? Predrawn syringes stay stable for about one week when refrigerated. Store all insulin cool and out of direct sunlight.