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Chapter: Clinical Anesthesiology: Clinical Pharmacology: Adrenergic Agonists & Antagonists

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Adrenergic Agonists: Epinephrine

Epinephrine is an endogenous catecholamine syn-thesized in the adrenal medulla.

EPINEPHRINE

Clinical Considerations

Epinephrine is an endogenous catecholamine syn-thesized in the adrenal medulla. Direct stimulation of β1-receptors of the myocardium by epinephrine raises blood pressure, cardiac output, and myocar-dial oxygen demand by increasing contractility and heart rate (increased rate of spontaneous phase IV depolarization). α1-stimulation decreases splanch-nic and renal blood flow but increases coronary perfusion pressure by increasing aortic diastolic pressure. Systolic blood pressure rises, although β2-mediated vasodilation in skeletal muscle may lower diastolic pressure. β2-stimulation also relaxes bron-chial smooth muscle.

Administration of epinephrine is the princi-pal pharmacological treatment for anaphylaxis and can be used to treat ventricular fibrillation. Com-plications include cerebral hemorrhage, coronary ischemia, and ventricular dysrhythmias. Volatile anesthetics, particularly halothane, potentiate the dysrhythmic effects of epinephrine.

Dosing & Packaging

In emergency situations (eg, cardiac arrest and shock), epinephrine is administered as an intrave-nous bolus of 0.05–1 mg, depending on the severity of cardiovascular compromise. In major anaphylac-tic reactions, epinephrine should be used at a dose of 100–500 mcg (repeated, if necessary) followed by infusion. To improve myocardial contractil-ity or heart rate, a continuous infusion is prepared (1 mg in 250 mL [4 mcg/mL]) and run at a rate of 2–20 mcg/min. Epinephrine is also used to reduce bleeding from the operative sites. Some local anes-thetic solutions containing epinephrine at a con-centration of 1:200,000 (5 mcg/mL) or 1:400,000 (2.5 mcg/mL) are characterized by less systemic absorption and a longer duration of action. Epi-nephrine is available in vials at a concentration of 1:1000 (1 mg/mL) and prefilled syringes at a con-centration of 1:10,000 (0.1 mg/mL [100 mcg/mL]). A 1:100,000 (10 mcg/mL) concentration is available for pediatric use.

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