What is the mechanism of action for an epinephrine auto-injector (EpiPen)?

An epinephrine auto-injector, commonly known as an EpiPen, is designed to treat severe allergic reactions, or anaphylaxis, by rapidly reversing the symptoms of such reactions. One of the primary mechanisms of action of epinephrine is its ability to combat the effects of vasodilation and low blood pressure by causing vasoconstriction.

When someone experiences anaphylaxis, their blood vessels dilate excessively, leading to a drop in blood pressure and reduced blood flow to vital organs. This vasodilation can result in shock if not addressed promptly. Epinephrine works by binding to alpha-adrenergic receptors in the vascular smooth muscle, leading to vasoconstriction, which helps increase blood pressure and restore adequate blood circulation.

Additionally, epinephrine also stimulates beta-adrenergic receptors, which can increase heart rate and enhance myocardial contractility, but its primary role during anaphylaxis, particularly with an EpiPen, is to address the vasodilation and associated hypotension that occur during these acute allergic events. This makes the role of vasoconstriction crucial in stabilizing the patient's condition.