Epinephrine

Introduction Overview

Generic Name

Epinephrine

Brand Name

Adrenaclick, Adrenalin, Auvi-Q, EpiPen

Dosage Form

Parenteral injection (IM, Sub-Q, IV, IO), prefilled auto-injector, topical solution

Drug Class

Alpha- and Beta-Adrenergic Agonists

Pharmacokinetics

Absorption:
Epinephrine is rapidly absorbed following subcutaneous (Sub-Q) or intramuscular (IM) injection, with absorption augmented by massaging the injection site to enhance systemic uptake. After oral ingestion, epinephrine is extensively metabolized in the gastrointestinal tract and liver, resulting in negligible systemic bioavailability and absence of pharmacologically active plasma concentrations. Endotracheal administration permits absorption through the lung capillary bed, although serum concentrations reach only about 10% of those attained with equivalent intravenous dosing, limiting systemic effects. Bronchodilation typically occurs rapidly, within 1 minute after oral inhalation, and within 5–10 minutes post Sub-Q injection in asthmatic attacks, with a short duration of action across parenteral and inhalation routes.

Distribution:
Epinephrine distributes extensively, crossing the placenta but does not readily cross the blood-brain barrier, preventing significant central nervous system effects. It is excreted into breast milk, warranting caution in nursing mothers. The drug distributes primarily to tissues innervated by sympathetic nerves, except the sweat glands and arteries of the face, reflecting its adrenergic receptor specificity.

Metabolism:
The pharmacologic actions of epinephrine are rapidly terminated mainly via uptake and enzymatic metabolism within sympathetic nerve endings and systemically in hepatic and other tissues. Key enzymes involved are catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), which metabolize epinephrine to inactive metabolites. This rapid metabolism accounts for its short half-life and duration of action, necessitating repeated or continuous dosing for sustained effect.

Elimination:
Approximately 40% of administered epinephrine is excreted in the urine primarily as inactive metabolites, reflecting extensive hepatic and extraneuronal metabolism. The elimination kinetics contribute to the need for repeated administration in emergencies. Renal excretion represents the major elimination route of metabolites rather than intact drug.

Dosage Forms

Available Dosage Forms:
- Parenteral Injection (IM, Sub-Q, IV, IO):
- 0.1 mg/mL (e.g., EPINEPHrine Injection, available in prefilled syringes)
- 0.5 mg/mL (EpiPen Jr. Auto-Injector delivers 0.15 mg in 0.3 mL)
- 1 mg/mL (Adrenaclick Auto-Injector available in 0.15 mg (0.15 mL) and 0.3 mg (0.3 mL) doses)
- Prefilled Auto-Injectors:
- EpiPen Auto-Injector (0.3 mg in 0.3 mL)
- Auvi-Q Auto-Injector (0.15 mg or 0.3 mg doses)
- Topical Solutions: Concentrations range from 0.002% to 0.1% for local hemostasis and vasoconstriction.

Dosages for Adults and Adolescents:
- Anaphylaxis (IM/Sub-Q): 0.2–0.5 mg every 5–15 minutes as needed; self-administered auto-injector dose typically 0.3 mg.
- Cardiac Arrest (IV/IO): 1 mg every 3–5 minutes during resuscitation.
- Bradycardia (IV infusion): 2–10 mcg/min, titrated to response.
- Septic Shock (IV infusion): 0.05–2 mcg/kg/min, titrated to blood pressure.
- Bronchospasm (Severe asthma) Sub-Q: 0.3–0.5 mg every 20 minutes up to 3 doses.
- Adjunct to local anesthesia: local injection concentrations 0.002–0.02 mg/mL (commonly 0.005 mg/mL).

Specific Patient Populations:
- Pediatric Patients: Dosing individualized by weight for anaphylaxis IM/Sub-Q (0.01 mg/kg up to 0.3–0.5 mg/dose), with auto-injector dosing at 0.15 mg (15–30 kg) or 0.3 mg (≥30 kg). IV/IO dosing in resuscitation at 0.01 mg/kg every 3–5 minutes, max single dose 1 mg.
- Neonates may require lower concentrations and dosing adjustments due to sensitivity.
- Geriatric Use: Requires caution due to increased risk of adverse cardiovascular effects.
- Special handling and dilution protocols apply for IV administration to avoid overdose and tissue necrosis.

Mechanism Of Action

Epinephrine is an endogenous catecholamine acting as a potent agonist at both alpha (α) and beta (β) adrenergic receptors, exerting diverse physiological effects through these receptor-mediated pathways. At the molecular level, epinephrine binds to G protein-coupled adrenergic receptors distributed widely across tissues innervated by the sympathetic nervous system, excluding sweat glands and select vasculature.

The primary action at β2-adrenergic receptors in bronchial smooth muscle induces relaxation by increasing intracellular cyclic AMP via activation of adenylate cyclase. This causes bronchodilation, relieving bronchospasm and improving airflow, important in emergent asthma exacerbations and anaphylactic respiratory distress. Simultaneously, epinephrine constricts bronchial arterioles via α-adrenergic receptor activation, reducing mucosal edema and nasal congestion.

Epinephrine’s stimulatory effects on β1-adrenergic receptors in cardiac myocytes enhance myocardial contractility (positive inotropy) and increase heart rate (positive chronotropy) via increased cyclic AMP-mediated calcium influx. This results in augmented cardiac output and oxygen consumption, beneficial for restoring circulation during cardiac arrest and hypotensive shock states.

It causes vasoconstriction in skin, mucous membranes, and visceral arterioles by activating α-adrenergic receptors, reducing cutaneous blood flow and aiding local hemostasis when applied topically. At the same time, epinephrine promotes glycogenolysis in hepatic tissue and inhibits pancreatic insulin secretion, leading to increased blood glucose levels during stress responses.

Clinically, these combined mechanisms allow epinephrine to rapidly reverse life-threatening anaphylactic reactions through bronchodilation, vasoconstriction to restore vascular tone, and cardiac stimulation to maintain perfusion. Compared to selective β2-agonists, epinephrine has a broader receptor profile impacting multiple organ systems, with a rapid onset but shorter duration requiring prompt and repeated dosing or continuous infusions during emergencies. Its multifaceted receptor activity underpins its critical role in advanced cardiac life support protocols and anaphylaxis management.

Pharmacological Actions

Stimulation of both α- and β-adrenergic receptors causing widespread sympathetic activation.
Bronchodilation via β2-adrenergic receptor activation relaxing bronchial smooth muscle.
Cardiac stimulation with increased heart rate and contractility via β1-adrenergic receptors.
Peripheral vasoconstriction through α-adrenergic receptor activation promoting increased systemic vascular resistance.
Reduction of histamine release and antagonism of histamine’s effects on target organs.
Increase in glycogenolysis and inhibition of insulin release leading to transient hyperglycemia.
Local vasoconstriction for hemostasis when applied topically to small vessels.
Positive chronotropic and inotropic effects improving cardiac output in shock and cardiac arrest.
Rapid onset of action with short duration necessitating repeat dosing or continuous infusion.
Modulation of airway edema and congestion via vascular effects.
Potential to induce arrhythmias due to cardiac excitatory effects.
Anti-allergic properties through multiple receptor-mediated pathways.
Vasopressor activity raising aortic diastolic pressure to enhance coronary and cerebral perfusion during resuscitation.
Use in combination with local anesthetics to prolong anesthesia and reduce systemic absorption.

Therapeutic Or Clinical Uses

Emergency treatment of severe acute anaphylaxis including anaphylactic shock.
Management of anaphylactic symptoms such as urticaria, angioedema, hypotension, and respiratory distress.
Advanced Cardiac Life Support (ACLS) for cardiac arrest to facilitate return of spontaneous circulation (ROSC).
Treatment of symptomatic bradycardia in adults and children when unresponsive to atropine.
Vasopressor support to manage hypotension in septic shock as second-line therapy.
Adjunct local vasoconstriction in combination with local anesthetics to prolong anesthesia duration.
Topical application to control superficial bleeding from small vessels.
Use in premature labor as a tocolytic agent (off-label) though limited due to adverse effects.
Temporary bronchodilation in severe asthma exacerbations (IV or sub-Q), although less preferred compared to selective β2-agonists.
Endoscopic injection for hemostasis in nonvariceal upper gastrointestinal hemorrhage (off-label use).
Management of allergic reactions caused by insect stings, foods, drugs, latex, and other allergens.
Use during ACLS to improve coronary and cerebral perfusion pressures.
Post-resuscitation stabilization to optimize blood pressure and cardiac output.
Bradycardia treatment in pediatric patients with cardiopulmonary compromise.
Emergency self-administration in anaphylaxis via auto-injector devices.

Side Or Adverse Effects

Tachycardia, palpitations, and arrhythmias including potentially fatal ventricular fibrillation.
Hypertension potentially causing cerebral hemorrhage or aortic rupture.
Anxiety, fear, restlessness, nervousness, and tremors.
Headache, dizziness, weakness, and lightheadedness.
Nausea, vomiting, sweating, and pallor.
Respiratory difficulties including apnea and potential rebound bronchospasm post inhalation.
Tissue necrosis and local ischemia at injection or infusion sites due to vasoconstriction.
Increased myocardial oxygen consumption potentially aggravating angina pectoris.
ECG alterations including T-wave changes and cardiac rhythm disturbances.
Exacerbation or induction of psychomotor agitation, hallucinations, and psychosis.
Severe metabolic acidosis with prolonged or excessive use.
Increased rigidity and tremor in patients with Parkinson's disease.
Possible hypersensitivity reactions to sulfites present in some formulations.
Local extravasation injury risks requiring prompt intervention with phentolamine mesylate.
Potential worsening of glycemic control in diabetic patients via hyperglycemia induction.

Precautions

Extreme caution in patients with cardiovascular diseases including coronary artery disease, arrhythmias, and hypertension.
Correction of hypovolemia before administration as vasopressors are ineffective without adequate blood volume.
Close monitoring for extravasation during IV infusion to prevent tissue necrosis.
Careful titration during IV administration, particularly in elderly or fragile patients.
Use with caution in patients with hyperthyroidism due to increased susceptibility to adverse effects.
Consider alternative therapies or adjuncts in patients taking β-adrenergic blockers due to potential antagonism.
Avoid IM injections in buttock; preferred site is anterolateral thigh for optimal absorption.
Storage as per manufacturer’s guidelines to avoid degradation and loss of potency.
Avoid concomitant use with general anesthetics like cyclopropane or halogenated hydrocarbons due to increased arrhythmia risk.
Monitoring and caution with concomitant use of MAO inhibitors, tricyclic antidepressants, and other interacting drugs.
Caution during pregnancy; use only if clearly indicated due to possible uterine blood flow effects.
Patients with Parkinson’s disease may experience transient worsening of symptoms.
Patients should be advised on correct administration technique and proper use of auto-injectors.
Monitoring for rebound symptoms and prolonged observation after anaphylaxis treatment is advisable.
Avoid use in cardiogenic, hemorrhagic, or traumatic shock due to potential for harm.

Warnings

Risk of causing serious cardiovascular events including angina, myocardial infarction, cerebral hemorrhage from abrupt hypertension.
Extravasation can cause severe local tissue necrosis requiring immediate treatment.
Use extreme caution in patients receiving general anesthesia with sensitizing agents such as halothane or cyclopropane.
Potential for paradoxical worsening in asthmatic patients with sulfite sensitivity present in some preparations.
Risk of serious cardiac arrhythmias even in patients without preexisting heart disease.
Avoid inadvertent IV administration of concentrated solutions intended for IM use due to overdose risks.
Do not use epinephrine as a substitute for volume replacement in shock states.
Careful titration and monitoring recommended during IV infusion due to interindividual variability in response.
Warning against injection into fingers, toes, ears, nose, or other end-artery areas due to risk of ischemia.
Post-administration monitoring for biphasic or recurrent anaphylaxis; observation time of 4–8 hours recommended for moderate to severe cases.
Avoid use in patients with angle-closure glaucoma and organic brain damage unless benefits outweigh risks.
High-dose epinephrine does not improve survival in cardiac arrest beyond standard dosing and may be harmful.
Potential enhancement of adverse cardiac effects when administered with certain drugs like digoxin or MAO inhibitors.
Excessive dosing may cause severe metabolic disturbances including lactic acidosis.
Pregnant women must be resuscitated promptly despite potential uterine blood flow reduction to ensure fetal survival.

Contraindication

No absolute contraindications exist for use in life-threatening situations such as anaphylaxis and cardiac arrest.
Relative contraindications include shock states other than anaphylactic and septic shock.
Known hypersensitivity to sympathomimetic amines.
Coronary insufficiency and cardiac dilatation due to risk of exacerbated ischemia.
Use with caution or contraindicated in patients with angle-closure glaucoma or organic brain damage.
Avoid use during general anesthesia with sensitizing agents such as cyclopropane and halogenated hydrocarbon anesthetics (e.g., halothane).
Contraindicated for use with local anesthetics in digit blocks (e.g., fingers, toes, ears) due to risk of ischemic tissue necrosis.
Avoid use in cardiogenic shock and hemorrhagic or traumatic shock owing to detrimental hemodynamic effects.
Relative contraindication for patients with severe hypertension unless benefits outweigh risks.
Avoid concomitant use with drugs having additive sympathomimetic effects to minimize toxicity.
Use cautiously or avoid in patients with documented arrhythmias or predisposition to ventricular fibrillation.
Known sensitivity to sulfites present in some formulations may be a relative contraindication.
Patients with untreated pheochromocytoma except in emergent critical care settings.
Severe coronary artery disease where cardiac stimulation poses significant risk.
Avoid use in intrathecal or epidural administration due to neurotoxicity potential.

Drug Interactions

Alpha-adrenergic blockers (e.g., phentolamine) antagonize vasoconstrictive and hypertensive effects of epinephrine.
Beta-adrenergic blockers (e.g., propranolol) antagonize cardiac and bronchodilatory effects, may potentiate pressor response.
General anesthetics like halogenated hydrocarbons and cyclopropane increase myocardial sensitization to arrhythmias with epinephrine.
Monoamine oxidase inhibitors (MAOIs) inhibit epinephrine metabolism, potentially causing severe prolonged hypertension.
Tricyclic antidepressants potentiate cardiac effects, increasing risk of tachyarrhythmias.
Antidiabetic agents may require adjustment as epinephrine induces hyperglycemia and antagonizes insulin.
First-generation antihistamines may enhance epinephrine’s cardiac stimulation.
Antihypertensives antagonize epinephrine's pressor effects, potentially reducing efficacy.
Catechol-O-methyltransferase (COMT) inhibitors increase and prolong epinephrine effects.
Clonidine potentiates hypertensive effects requiring careful monitoring.
Corticosteroids potentiate hypokalemic effects, increasing risk of electrolyte imbalance.
Digoxin increases myocardium sensitivity, raising risk of arrhythmia when combined with epinephrine.
Diuretics antagonize pressor effects and may potentiate arrhythmogenic and hypokalemic effects.
Doxapram potentiates pressor effects; caution warranted.
Ergot alkaloids may oppose epinephrine-induced vasoconstriction.
Nitrates antagonize epinephrine’s pressor effects, possibly reducing blood pressure.
Oxytocics may cause severe persistent hypertension when used concomitantly.
Phenothiazines reverse vasopressor effect and should not be used for phenothiazine-induced hypotension.
Quinidine may potentiate arrhythmogenic risks.
Other sympathomimetic amines have additive effects increasing toxicity risk.
Theophylline potentiates epinephrine-induced hypokalemia.
Thyroid hormones potentiate epinephrine cardiac effects.

Preparations Of The Drug

EPINEPHrine Injection: Solution 0.1 mg/mL available in prefilled syringes for IM or Sub-Q use.
EpiPen Jr. Auto-Injector: Delivers a single 0.15 mg (0.3 mL) dose for pediatric use.
Adrenaclick Auto-Injector: Available in 0.15 mg (0.15 mL) and 0.3 mg (0.3 mL) doses for emergency IM injection.
Adrenalin: Parenteral injection 1 mg/mL used for various emergency indications.
Auvi-Q Auto-Injector: Voice-guided device available in 0.15 and 0.3 mg doses for anaphylaxis self-administration.
EpiPen Auto-Injector: Standard adult dose of 0.3 mg (0.3 mL) in an easy-to-use prefilled device.
Topical aqueous solutions ranging from 0.002% to 0.1% for vasoconstriction and hemostasis of superficial bleeding.
Prefilled syringes and multi-dose vials with nitrogen replacement to improve stability and reduce oxidation.
Auto-injectors provided with manufacturer’s patient instructions and safety carrying cases.
Parenteral solutions require protection from light and air to prevent oxidation; slight discoloration or precipitation mandates disposal.
Diluents such as normal saline used for preparing dilute solutions for IV infusions.
Various commercial products differ in preservatives and excipients; consult specific product labeling for details.
Standardized concentrations established for continuous IV infusion dosing, adjusted for adult and pediatric patients.
Storage recommendations generally include protection from light, avoidance of freezing or extreme heat.
Auto-injectors should not be refrigerated or frozen but may be stored between 15–30°C.