Epinephrine is one of the most commonly used agents in a variety of settings as it functions as medication and hormone. It is currently FDA-approved for various situations, including emergency treatment of type 1 hypersensitivity reactions including anaphylaxis, induction, and maintenance of mydriasis during intraocular surgeries, and hypotension due to septic shock. Off-label uses of epinephrine include, but are not limited to, ventricular fibrillation, pulseless ventricular tachycardia, asystole, pulseless electrical activity, croup, and severe asthma exacerbations unresponsive to standard treatment. In the operating room (OR) setting, epinephrine is used as a local anesthetic block as well. Produced by the adrenal medulla, epinephrine plays a vital role in the body’s acute stress response by stimulating the sympathetic nervous system.
Epinephrine is a sympathomimetic catecholamine that exerts its pharmacologic effects on both alpha and beta-adrenergic receptors using a G protein-linked second messenger system. It has a greater affinity for beta receptors in small doses. However, large doses produce selective action on alpha receptors. Through its action on alpha-1 receptors, epinephrine induces increased vascular smooth muscle contraction, pupillary dilator muscle contraction, and intestinal sphincter muscle contraction. Other important effects include increasing heart rate, myocardial contractility, and renin release via beta-1 receptors. Beta-2 effects produce bronchodilation which may be useful as an adjunct treatment of asthma exacerbations as well as vasodilation, tocolysis, and increased aqueous humor production.
Depending on the diagnosis, epinephrine can be given in various forms. For the treatment of anaphylaxis, epinephrine is preferably injected intramuscularly into the anterolateral aspect of the thigh due to rapid absorption or subcutaneously as well. For advanced cardiovascular life support (ACLS), epinephrine may be given intravenously or intraosseous if needed. Another route of administration is through an endotracheal tube often used in neonatal resuscitation.
Adverse Effects Listed by System
The more common side effects include tachycardia, hypertension, headache, anxiety, apprehension, palpitations, diaphoresis, nausea, vomiting, weakness, and tremors.
Careful monitoring of vital signs is crucial especially in patients with polypharmacy.
There are no absolute contraindications against using epinephrine. Some relative contraindications include hypersensitivity to sympathomimetic drugs, closed-angle glaucoma, anesthesia with halothane. As is the case with prescribing any medication, all practitioners should use clinical judgment and evaluate the benefits versus risk with epinephrine.
The use of epinephrine in select circumstances must be assessed as discussed below.
Epinephrine is considered a pregnancy Category C medication. There are no well-controlled studies in humans, although animal studies have shown a teratogenic risk during organogenesis. It is capable of crossing the placenta. Gastroschisis has been demonstrated when epinephrine has been administered subcutaneously in rabbits at 15 times the maximum dosage. Epinephrine should be used cautiously when maternal blood pressure is 130/80 mm Hg and greater.
Labor and Delivery
Due to its effect on beta-2 adrenergic receptors causing tocolysis, epinephrine opposes the actions of oxytocin on the uterus and may delay labor. It must also be used with caution during anaphylaxis induced hypotension in pregnancy as it may lead to uterine vasoconstriction, thus decreasing oxygen delivery to the fetus.
More clinical studies are needed to determine if epinephrine is excreted through breast milk.
Epinephrine is effective at a dilution of 1:100,000 to 1:400,000 for mydriasis induction and maintenance in pediatric intraocular surgeries.
Due to the expected decrease in renal, hepatic, and cardiac function of geriatric patients, epinephrine should be started at the lower end of the dosing regime and titrated appropriately for clinical effect.
Several locations should be avoided when injecting epinephrine specifically the digits, nose, penis, and toes as these areas are more prone to ischemia. Epinephrine should be avoided in tissues supplied by end arteries.
When administered parenterally, epinephrine has a rapid onset, but short duration of action. When given intravenously, it has a half-life of fewer than 5 minutes. It is primarily metabolized in the liver along with various other locations such as the kidneys, skeletal muscle, and mesenteric organs. It is degraded into an inactive metabolite named vanillylmandelic acid by MAO and COMT and excreted into the urine. However, a small amount of the drug is excreted unchanged as well.
Epinephrine is a hormone that produces widespread effects. Certain effects need to be monitored. Tachycardia and hypertension are expected when epinephrine is given intravenously, so it is important to titrate carefully while monitoring hemodynamics. Epinephrine is also used with anesthetic agents to provide analgesia. In locations where extravasation of epinephrine has occurred, prevention and treatment of ischemia-induced necrosis are necessary. The infiltrated area should be treated with 10 mL to 15 mL saline solution containing 5 mL to 10 mg of phentolamine, an alpha-adrenergic blocking agent.
Renal impairment must be monitored as epinephrine causes renal blood vessel constriction and can decrease urine impairment. In patients with chronic kidney disease and various other renal pathologies, clinical judgment should be exercised. During intraocular use, epinephrine must be diluted otherwise corneal endothelial damage can result if undiluted concentrations of sodium bisulfite are administered.
Administration of excess epinephrine that leads to supra-therapeutic levels may cause predictable adverse effects that warrant supportive treatment. Overdose may cause elevated arterial pressures leading to cerebrovascular accidents. Pressor effects can be minimized by the usage of an alpha-adrenergic blocker or by the usage of vasodilators such as nitrites. Pulmonary edema has also been noted due to the underlying mechanism of peripheral vasoconstriction along with myocardial stimulation. Respiratory support may be needed alongside an alpha-adrenergic blocking drug to decrease vasoconstriction and enhance vascular flow. Due to strong beta-1 adrenergic effects on cardiac tissue, epinephrine toxicity may lead to potentially fatal cardiac arrhythmias or ischemia. Treatment involves administration of beta-adrenergic blocking agents such as metoprolol.