Epinephrine, also known as adrenaline, is a naturally occurring hormone in the body that also serves as an emergency medication. It is widely recognized as the most effective treatment for severe allergic reactions, anaphylaxis. It acts swiftly to counteract the body’s extreme response to an allergen, providing a temporary but critical intervention.
How Epinephrine Works in the Body
Epinephrine plays a role in the body’s immediate “fight-or-flight” response, preparing the system to react to perceived threats. As a medication, it acts on various receptors throughout the body, triggering physiological changes. It stimulates the heart to beat faster and with greater force, increasing blood pressure and improving circulation.
It also relaxes airway muscles, opening them to make breathing easier and reducing swelling that can restrict airflow. Simultaneously, it constricts blood vessels, maintaining blood pressure and redirecting blood flow to vital organs and muscles. These combined actions effectively reverse severe allergic reaction symptoms, such as swelling, hives, and a dangerous drop in blood pressure.
Typical Duration of Epinephrine’s Effects
Epinephrine has a rapid onset of action. However, its effects are short-lived. Following an injection, such as with an auto-injector, effects last about 10 to 20 minutes.
The body rapidly processes epinephrine, with a plasma half-life often less than 5 minutes. While epinephrine provides immediate symptom relief, this relief is temporary.
Variables Affecting How Long Epinephrine Lasts
Several factors influence how long the effects of administered epinephrine persist. The dose given is one variable; higher doses can lead to greater peak concentrations of the medication in the bloodstream. The method by which epinephrine is delivered also plays a role in its absorption and duration.
Intramuscular (IM) injection, such as with an auto-injector into the outer thigh, allows rapid absorption due to the rich blood supply in muscle tissue. In contrast, subcutaneous injection, which delivers the medication just under the skin, results in slower absorption because subcutaneous tissues have less vascularity. Intravenous (IV) administration, used in a hospital setting, provides immediate systemic availability, though the drug is also cleared very quickly.
An individual’s metabolism also affects how quickly epinephrine is broken down in the body. Enzymes like Catechol-O-methyltransferase (COMT) and Monoamine Oxidase (MAO) metabolize epinephrine, and variations in their activity can alter the drug’s duration. The severity of the condition being treated, such as the intensity of an allergic reaction, can also influence the perceived duration of epinephrine’s effects. A more severe reaction might require more drug to manage, potentially making its effects seem to wear off sooner.
What to Do After Epinephrine Administration
Administering epinephrine is an immediate step in managing a severe allergic reaction, but it is not the final step. Call emergency services, such as 911, immediately after epinephrine has been given, even if symptoms appear to improve. The effects of the medication are temporary, and ongoing medical evaluation and treatment are necessary.
Individuals who have received epinephrine should be transported to an emergency facility for observation, for at least 4 to 6 hours or longer, depending on the severity of their initial reaction. This monitoring period is crucial due to the risk of a biphasic reaction, where symptoms return after an initial improvement without further exposure to the allergen. These secondary reactions can occur hours after the first episode, sometimes up to 72 hours later, and their severity varies.
If symptoms persist 5 to 15 minutes after the first dose, or if they return, a second dose may be necessary. However, additional doses beyond two should only be administered under the direct supervision of medical professionals. The individual should remain lying down, if possible, and avoid eating or drinking immediately after receiving epinephrine. The used auto-injector should be given to emergency responders for assessment and disposal.