What Is Epinephrine?

Epinephrine, also known as adrenaline, is a powerful stress hormone and neurotransmitter that is produced by the adrenal glands. It plays a vital role in the body’s acute stress response by stimulating the sympathetic nervous system.

Epinephrine is involved in various important functions throughout the body such as breathing, muscle contractions, and the fight or flight response. It can also be used as a drug due to its various important functions.

What Is Epinephrine Used For?

Epinephrine is currently FDA-approved for various situations, including emergency treatment of type 1 hypersensitivity reactions such as anaphylaxis after allergic reactions and severe low blood pressure, or hypotension, due to septic shock.

In addition to these indications, epinephrine is the primary drug administered during cardiopulmonary resuscitation (CPR) to reverse cardiac arrest. Dosage delivery routes for epinephrine include intravenous, inhalation, nebulization, intramuscular injection, and subcutaneous injection.

Anaphylaxis is an acute and potentially lethal multisystem allergic reaction. Most consensus guidelines for the past 30 years have held that epinephrine is the drug of choice and the first drug that should be administered in acute anaphylaxis.

Epinephrine is commonly used to counteract the effects of severe allergic reactions. The EpiPen, an auto-injector form of epinephrine, has been available in the USA since 1987. On August 16, 2018, Teva Pharmaceuticals USA received approval to market its generic epinephrine auto-injector in 0.3 milligram (mg) and 0.15 mg strengths. In 2024, the FDA approved Neffy (epinephrine nasal spray).

Off-label uses of epinephrine include, but are not limited to, ventricular fibrillation, pulseless ventricular tachycardia, asystole (lack of heartbeat), pulseless electrical activity (PEA), croup, and severe asthma exacerbations unresponsive to standard treatment.

How Epinephrine Works

Epinephrine is a sympathomimetic catecholamine that exerts its pharmacologic effects on both alpha and beta-adrenergic receptors. It has a dose-dependent response on alpha and beta receptors that leads to different pharmacological effects in the body.

It has a greater affinity for beta receptors in small doses, but in larger doses, it produces more selective action on alpha receptors. Its impact on alpha-1 receptors leads to increased vascular smooth muscle contraction, pupillary dilator muscle contraction, and intestinal sphincter muscle contraction.

Its impact on beta-1 receptors leads to increased heart rate, myocardial contractility, and renin-release. Stimulation of beta-2 receptors leads to bronchodilation, which may be useful as an adjunct treatment of asthma exacerbations as well as vasodilation, tocolysis, and increased aqueous humor production.

Epinephrine works to alleviate anaphylaxis by relaxing the smooth muscles of the bronchi found in your lungs. It is also helpful in conditions such as asthma due to its ability to relieve bronchospasm (airways constrict), wheezing, and dyspnea (shortness of breath).

How to Administer Epinephrine

Epinephrine is administered differently depending on its reason for use. To treat anaphylaxis, it is best to inject epinephrine in the muscle, preferably the thigh, due to rapid absorption. It's important to note that epinephrine's half-life is approximately two to three minutes.

When administered by subcutaneous or intramuscular injection, local vasoconstriction may occur after the drug has been rapidly absorbed, delaying absorption which results in epinephrine's effects lasting longer than the half-life suggests.

For advanced cardiovascular life support (ACLS), patients can receive epinephrine intravenously or intraosseous (via the bone) if needed. Another route of administration is through an endotracheal tube often used in neonatal resuscitation.

When to Administer Epinephrine

If you notice someone experiencing anaphylactic symptoms such as lightheadedness, dizziness, difficulty breathing or wheezing, hives, nausea, vomiting, tongue swelling, difficulty swallowing, facial swelling, or mental confusion they may be having a life-threatening allergic reaction.

Medical expert consensus believes that there is no absolute contraindication to epinephrine administration in anaphylaxis. It can be administered in doses appropriate for the severity of the reaction, regardless of the initial signs and symptoms of anaphylaxis.

All subsequent therapeutic interventions depend on the initial response to epinephrine. Development of toxicity or inadequate response to epinephrine injections indicates that additional therapeutic modalities are necessary.

Side Effects of Epinephrine

The most common side effects after taking epinephrine are:

• Tachycardia
• Hypertension
• Headache
• Anxiety
• Heart palpitations
• Diaphoresis
• Nausea
• Vomiting
• Weakness
• Tremors

When Not To Use Epinephrine

While there are no absolute contraindications against using epinephrine, it is important to note that the hormone interacts with many other drugs, therefore it is important to consult a medical professional for all non-emergency use of the drug.

Some relative contraindications include hypersensitivity to sympathomimetic drugs, closed-angle glaucoma, and anesthesia with halothane. Another unique contraindication to be aware of is catecholaminergic polymorphic ventricular tachycardia.

As is the case with taking any drug, you and your provider should evaluate the benefits versus risks of taking epinephrine.

Anaphylaxis Precautions

As previously stated epinephrine's most common use is to treat acute anaphylaxis. Proper and timely epinephrine use can be life-saving. Anaphylaxis can be fatal so it is crucial to optimize prevention in anyone at risk of allergic disease.

Ways for you to reduce the risk of anaphylaxis include:

• Carry a food or drug allergy list.
• Ask to read food and medication labels.
• Avoid foods that may cause an allergic reaction.
• Meet with an allergy specialist if possible.
• Optimally manage asthma and coronary artery disease.
• Avoid mixing medications.

An allergist-immunologist can provide comprehensive professional advice on these matters and should be consulted if they are not already involved in the anaphylaxis plan of care. All patients at risk for future anaphylaxis should carry at least one epinephrine syringe and know how to administer it. Ideally, they should carry two to use in case symptoms do not decline after a few minutes. EpiPens come in packs of two.