Phenylephrine

Provider Level

RN/Paramedic

Class

Sympathomimetic, Alpha-1 Adrenergic Agonist, Vasopressor

Mechanism of Action

Direct-acting pure alpha-1 adrenergic receptor agonist. Causes potent peripheral vasoconstriction, increasing systemic vascular resistance and blood pressure without significant direct chronotropic or inotropic effects.

Indications

Distributive shock (e.g., neurogenic shock, septic shock), anesthesia-induced hypotension, and severe hypotension when vascular tone is low but cardiac output is adequate.

Contraindications

Severe hypertension, ventricular tachycardia, cardiogenic shock, known hypersensitivity to the drug or sulfites.

Routes

IV, IO

Onset / Duration

Onset: Immediate. Duration: 15-20 minutes.

Adverse Effects

Reflex bradycardia, severe hypertension, headache, excitability, arrhythmias, myocardial ischemia, tissue necrosis with extravasation.

Precautions & Interactions

Extravasation can cause severe tissue necrosis. Use cautiously in patients with hyperthyroidism, severe arteriosclerosis, existing bradycardia, or myocardial disease.

Special Considerations

Requires continuous cardiac and blood pressure monitoring. Administer via a large vein or central line if possible to minimize extravasation risk. May cause reflex bradycardia which can decrease cardiac output. Phentolamine is the standard antidote for tissue extravasation.