Epinephrine
- Class: Adrenergic agonist
- Used for: anaphylaxis
- Say it: ep-ih-NEF-rin
- Forms: auto-injector, injection
EPINEPHRINE = the EPIPEN for the allergic EPISODE. One jab into the thigh and the airway opens, the vessels tighten, the pressure returns.
EPI-NEPHROS means upon the kidney, where the adrenal gland sits. In anaphylaxis it is the only drug that reverses the physiology — an antihistamine does nothing for a closing airway.
Alpha-1 tightens the leaking vessels and lifts the pressure, beta-2 opens the airway, beta-1 supports the heart. No antihistamine or steroid does any of this, which is why neither is a substitute.
Side effects
Common: fast heartbeat, shakiness, anxiety
Serious: arrhythmia, very high blood pressure
Typical dose
0.5 mg (0.5 mL of 1:1000) intramuscularly into the outer thigh
Repeat after 5 minutes if needed. 0.3 mg for ages 6–12. Intramuscular, never subcutaneous.
Check yourself
Why is adrenaline, rather than an antihistamine, the first treatment in anaphylaxis?
- It reverses the airway narrowing and the circulatory collapse within minutes
- It blocks histamine receptors more completely
- It prevents the allergen being absorbed
- It works slowly but lasts longer
Show answer
A. It reverses the airway narrowing and the circulatory collapse within minutes
An antihistamine blocks one mediator at one receptor and does nothing for a closing airway or a collapsing circulation. Adrenaline acts on alpha and beta receptors directly, treating the physiology rather than the chemistry.
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