From the Guidelines
The half-life of epinephrine (adrenaline) is approximately 2 minutes in the bloodstream. This extremely short half-life explains why epinephrine must be administered immediately in emergency situations like anaphylaxis or cardiac arrest, and why its effects are so rapid but brief. The body quickly metabolizes epinephrine primarily through the enzymes catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), which are found in various tissues including the liver and kidneys. Due to this rapid breakdown, epinephrine is typically administered as an injection rather than orally, as it would be destroyed by digestive enzymes before reaching the bloodstream.
Key Points
- The short half-life of epinephrine means that continuous infusions may be necessary to maintain therapeutic effects, and multiple doses may be required in emergency situations if symptoms persist or recur 1.
- The rapid metabolism also explains why the intense "fight-or-flight" physiological response triggered by naturally released epinephrine during stress subsides relatively quickly once the stressor is removed.
- Epinephrine has a narrow toxic-therapeutic index, and its administration can cause mild transient adverse effects, such as anxiety, fear, restlessness, headache, dizziness, palpitations, pallor, and tremor 1.
- In clinical settings, the short half-life of epinephrine requires careful monitoring and repeated dosing as needed to ensure effective treatment of anaphylaxis or other emergency conditions 1.
Administration Considerations
- Epinephrine can be delivered through a variety of routes, including IM, IV, and endotracheal or intraosseous 1.
- IM epinephrine is recommended over subcutaneous injection because it provides a more rapid increase in plasma and tissue concentrations of epinephrine 1.
From the Research
Half-Life of Epinephrine
- The half-life of epinephrine is approximately 4.1 minutes when administered via inhalation, as indicated by the elimination half-life in a study on inhaled epinephrine 2.
- However, the half-life of epinephrine can vary depending on the route of administration and other factors.
- For intramuscular administration, the maximal pharmacodynamic effect of epinephrine is reached within 10 minutes, but the exact half-life is not specified in the provided studies 3.
- Another study on the pharmacokinetics and pharmacodynamics of epinephrine after single and repeat administration of different delivery methods does not provide a specific half-life value 4.
Factors Affecting Half-Life
- The half-life of epinephrine can be influenced by various factors, including the route of administration, dosage, and individual patient characteristics.
- The absorption half-life of inhaled epinephrine is approximately 29 minutes, indicating that the drug is absorbed quickly into the bloodstream 2.
- The bioavailability of epinephrine after inhalation is subject to high interindividual and interoccasional variability, which can affect the half-life and overall efficacy of the drug 2.