4.15 Alpha- and Beta-Receptor Agonists (Catecholamines)

Epinephrine and Norepinephrine

Epinephrine and norepinephrine (NE) are adrenergics (also referred to as catecholamines) that stimulate the beta- and alpha-receptors on the target cell.

Mechanism of Action: Epinephrine acts on both alpha- and beta-adrenergic receptors and is used in several routes, including intravenously (IV), subcutaneously, intramuscularly, and inhalation. Epinephrine decreases vasodilation and increases vascular permeability through its alpha-adrenergic receptor action, which can lead to loss of intravascular fluid volume and hypotension. Through its action on beta-adrenergic receptors, epinephrine causes bronchial smooth muscle relaxation and helps alleviate bronchospasm, wheezing, and dyspnea that may occur during anaphylaxis.

Indications: Epinephrine is used for severe allergic reactions, acute bronchospasm during asthma attacks, cardiac resuscitation, hypotension in severe shock, or for local injection to control superficial bleeding.

Norepinephrine is used as a peripheral vasoconstrictor (due to alpha-adrenergic action) and as an inotropic stimulator of the heart and dilator of coronary arteries (due to beta-adrenergic action) in clients with critically low blood pressure.

Nursing Considerations: Epinephrine is contraindicated for use in fingers, toes, ears, nose, or genitalia when used with local anesthetic due to the vasoconstrictive action. It is also contraindicated in clients with narrow angle glaucoma. Administer with caution to the elderly and those with preexisting cardiovascular disease. Discard IV solution if discolored. When administering IV, monitor vitals (blood pressure, heart rate, and respiratory rate) and cardiovascular and respiratory systems closely; if blood pressure increases sharply, give rapid-acting vasodilators. Monitor IV site for extravasation. If extravasation occurs, immediately stop IV administration and follow agency policy. Phentolamine, an alpha-adrenergic antagonist, is the reversal agent used to reverse local vasoconstrictive effects if digital ischemia occurs.

Side Effects/Adverse Effects: Common side effects include hypertension and tachycardia.

Health Teaching & Health Promotion: Epinephrine formulated in a pen for injection is known as an EpiPen. An EpiPen is used for severe allergic reactions after exposure to an allergen such as a bee sting. Check expiration date, store at room temperature, and protect from light. Effects fade after 15-20 minutes, so seek medical care immediately.^[1]

Now let’s take a closer look at the medication grid on epinephrine and norepinephrine in Table 4.15a.^[2]

Table 4.15a Epinephrine and Norepinephrine Medication Grid

Dopamine

Dopamine is another type of catecholamine specifically used to improve perfusion of organs, improve cardiac output, and increase blood pressure. Dopamine has dose-dependent effects on targeted arteries in the kidneys, heart, and brain.

Mechanism of Action: In low doses, dopamine mainly stimulates dopamine receptors and dilates the renal vasculature. Moderate doses of dopamine stimulate beta-receptors for a positive inotropic effect. Higher doses also stimulate alpha-receptors, constricting blood vessels and increasing blood pressure.

Indications: Dopamine is used to treat shock, improve perfusion to vital organs, increase cardiac output, and correct hypotension.

Nursing Considerations: During infusion, frequently monitor blood pressure, cardiac output, urine output, and color and temperature of limbs. Dopamine can worsen cardiac ischemia and worsen chest pain for clients experiencing unstable angina or a myocardial infarction due to increased cardiac demand for oxygen. If urine flow decreases without hypotension, notify provider because dosage may need to be reduced. High doses of dopamine cause vasoconstriction and can cause adverse effects if extravasation occurs. Concurrent alpha- or beta-blockers can antagonize dopamine.

Side Effects/Adverse Effects: Common side effects include hypotension with low doses (due to vasodilatory effects) and hypertension in higher doses (due to vasoconstriction). Other side effects include tachycardia, palpitations, and dyspnea. Adverse effects include decreased blood flow to the extremities and decreased urine output.

Health Teaching & Health Promotion: Clients should contact their health care provider immediately if experiencing unusual sweating, dizziness, heart palpitations, or chest pain.

Now let’s take a closer look at the medication grid on dopamine in Table 4.15b.^[3]

Table 4.15b Dopamine Medication Grid