Phenylephrine

Emergency & Prehospital

• Post-induction or peri-intubation hypotension: Brief IV boluses for vasodilatory hypotension after induction or sedation. The FDA label covers anesthesia. EMS and ED push-dose use is per local protocol (see RSI).
• Vasodilatory hypotension when tachycardia is a problem: It raises BP without β₁ stimulation, and heart rate often falls in reflex. That is why it is preferred in severe aortic stenosis and obstructive HCM. A slower rate keeps diastolic filling and coronary perfusion.

ED / ICU / Transport

• Hypotension during anesthesia: Bolus or infusion when vasodilation is the main cause (FDA-labeled).
• Spinal anesthesia hypotension at cesarean delivery: The first-line vasopressor here. Run it as a prophylactic infusion with rescue boluses (obstetric anesthesia).
• Septic or other vasodilatory shock: Only an alternative or salvage vasopressor. It sits outside the Surviving Sepsis Campaign 2026 sequence, which runs norepinephrine first, adds vasopressin as norepinephrine escalates, then epinephrine. Use it for a specific reason: tachyarrhythmia limiting norepinephrine, norepinephrine unavailable, or refractory vasodilation with good cardiac output (labeled for septic shock on some 10 mg/mL generic labels)
• BP or cerebral perfusion pressure targets in neurocritical care (TBI, subarachnoid hemorrhage, acute spinal cord injury): per local neurocritical care protocol. Reach for it when tachycardia is unwanted, and not for bradycardic neurogenic shock (see Precautions).
• Acute hypotension in obstructive hypertrophic cardiomyopathy (HCM): The preferred vasoconstrictor once fluids fail. It has no inotropic effect, so it does not worsen outflow obstruction.
• Acute ischemic priapism: intracavernosal injection with corporal aspiration, with or without irrigation, as first-line treatment (off-label)

Other Uses

• Pediatric hypotension and hypercyanotic (tet) spells: Specialist use, in critical care and the operating room. Off-label in children.
• Nasal decongestant and ophthalmic mydriatic: Separate topical products, so this page does not cover them. The FDA proposed in 2024 to remove oral phenylephrine as an ineffective OTC decongestant.

The doses below follow the FDA labels. Where a current guideline differs, the row says so. Check the product and concentration before every use.

Available Forms

• Ready-to-use bolus: 100 mcg/mL in 5 mL (500 mcg) ampule or vial (Biorphen, Immphentiv) or 10 mL (1,000 mcg) vial (Immphentiv); do not dilute
• Concentrate: 10 mg/mL in 1 mL (10 mg) vial or ampule; pharmacy bulk vials of 5 mL (50 mg) and 10 mL (100 mg) are for pharmacy admixture only; must be diluted before any IV use
• Premixed bag: 20 mg in 250 mL 0.9% NaCl (80 mcg/mL), ready to use; labeled for hypotension during anesthesia only

Adult Dosing

Dosing weight: labels name no dosing weight for mcg/kg/min orders, so see Special Populations.

Pediatric Dosing

For first-line vasoactive choices, see Weight-Based Dosing and Pediatric Shock.

Continuous Infusion

Preparation & Administration

• Dilution: Ready-to-use 100 mcg/mL products and premixed bags need no dilution. For the 10 mg/mL concentrate, use D5W or 0.9% NaCl (label: 10 mg in 100 mL total = 100 mcg/mL for boluses; 10 mg in 500 mL = 20 mcg/mL for infusions). Throw out any colored or cloudy solution.
• Push: give the bolus through a running line, then flush; reassess BP before the next dose (every 1–2 min).
• Pump requirement: infusions on a smart pump with drug library, on a dedicated line or lumen; never flush an infusion line.
• Line: Extravasation causes necrosis. Use a large, free-flowing proximal vein and check the site often. Move to central access for prolonged or high-dose infusions. In septic shock, the Surviving Sepsis Campaign 2026 suggests starting vasopressors peripherally rather than delaying for central access (conditional, very low certainty). It sets no duration or dose limit for peripheral use.
• Before starting: correct volume depletion and acidosis where possible.

Renal and hepatic changes in response: see Special Populations.

Contraindications

• No absolute contraindication on several US labels. Biorphen and a few 10 mg/mL generics carry none. Others (e.g. Immphentiv and Hikma and Fresenius Kabi 10 mg/mL, the premixed bag) flag hypersensitivity to the product or its components.
• Cardiogenic shock or severe LV dysfunction as the sole vasopressor (relative). Afterload climbs and the heart rate drops, and together they can push cardiac output lower still.

Precautions

• Angina, heart failure or pulmonary arterial hypertension: it may make them worse.
• Bradycardia, AV block or β-blocker therapy: severe reflex bradycardia and reduced cardiac output can follow.
• Autonomic dysfunction (e.g. spinal cord injury): Expect an exaggerated pressor response. Start low.
• Neurogenic shock (cervical or high thoracic cord injury): Reflex bradycardia adds to unopposed vagal tone. In a bradycardic patient, norepinephrine or another β₁ agent is the better pick.
• Sulfite sensitivity: Some 10 mg/mL vials contain sodium metabisulfite. It can cause allergic-type reactions and severe asthma attacks, so check the product.
• Peripheral vascular disease: the risk of limb and visceral ischemia is higher.
• Hyperthyroidism: Patients are more sensitive to phenylephrine, and cardiotoxicity becomes a risk.
• Acidosis: may blunt phenylephrine (label). Correct it where possible.
• Septic shock: it may raise the need for renal replacement therapy. Monitor renal function.
• Oxytocic drugs (oxytocin, methylergonovine): the pressor effect is potentiated, and hemorrhagic stroke becomes a risk.

Hold / Reassess If

• BP above target: pause the boluses and back the infusion off. Taper it. Don't stop it cold.
• Heart rate falling with BP at or above goal: reduce the dose. If the bradycardia is symptomatic and BP is low, a different agent or atropine is what it needs.
• Low cardiac output signs despite a better MAP (mottling, urine output <0.5 mL/kg/hr, rising lactate): an agent with β₁ activity is worth considering.
• Swelling, blanching or pain at the IV site: shut that infusion down, restart in another vein and treat extravasation.

Common

• Reflex bradycardia (label frequencies not established)
• Hypertension, headache
• Nausea, vomiting
• Nervousness, tremor, paresthesia, excitability
• Pallor, sweating

Serious / Life-Threatening

Overdose & Toxicity Management

• Signs: rapid BP rise, headache, vomiting, reflex bradycardia, tingling of the extremities, ventricular extrasystoles or VT. Suspect a concentration error, such as a bolus drawn from the 10 mg/mL concentrate.
• Immediate: stop the drug. Infusion effects fade within minutes, with an effective half-life of about 5 min. A bolus may last up to 20 min.
• Antidote: No specific antidote. For severe hypertension, give an α-adrenergic antagonist (phentolamine). A pediatric phentolamine dose is set by a specialist and pharmacy, and this page does not establish one.

Clinically Significant Interactions

IV Compatibility

• Diluents: D5W or 0.9% NaCl (label). Diluted solution: use within 4 hr at room temperature or 24 hr refrigerated (2–8°C).
• Dedicated line or lumen: nothing gets bolused or flushed through the infusion line.
• Check an institutional compatibility resource.

• Pediatrics: The FDA label does not establish safety or effectiveness in children. Specialists use it off-label for hypotension and tet spells. See the Pediatric Dosing table.
• Neonates: No established dose. Only neonatal intensivists and pharmacy set dosing.
• Pregnancy: Cesarean-delivery trials and meta-analyses have found no drug-associated risk of major birth defects, miscarriage or low Apgar scores. There are no first- or second-trimester data. Animal studies showed lower fetal weight at doses below the human daily dose (0.4 times). Limb malformations and fetal deaths appeared in rabbits at 1.2 times the human daily dose or more. The point to hold onto: untreated hypotension cuts uteroplacental flow. Do not withhold it when indicated.
• Lactation: There are no data on presence in milk or effects on the infant. Weigh the benefits of breastfeeding against the mother's clinical need.
• Older Adults: Start at the low end of the dosing range. Bradycardia and ischemia risk is higher with coronary or vascular disease.
• Renal Impairment: End-stage renal disease makes patients more responsive. Start at the low end of the range and titrate to BP. In septic shock it may raise the need for renal replacement therapy.
• Hepatic Impairment: Cirrhosis (Child-Pugh B and C) blunts responsiveness. Start in the usual range, but expect to need more.
• Obesity / Dosing Weight: The label gives no guidance for mcg/kg/min dosing. Actual body weight raises the total dose, so some protocols use mcg/min orders or adjusted weight.

• Scope: Paramedics in some systems give push-dose phenylephrine, and so do RNs and critical-care transport (CCT) teams. Infusions are usually CCT or physician-directed. It varies by state and agency protocol.
• Storage & Stability: Store vials, ampules and bags at 20–25°C (68–77°F). Excursions to 15–30°C (59–86°F) are permitted. Keep vials in the carton to protect them from light. A syringe or bag diluted from the concentrate lasts only 4 hr at room temperature (24 hr refrigerated). Discard any bedside push-dose syringe you did not use.
• Carried Concentration: Your kit may carry any of these: 10 mg/mL concentrate, 100 mcg/mL bolus product, 80 mcg/mL premix or 20 mcg/mL diluted infusion. Keep the concentrate apart from the ready-to-use products, and label every syringe with mcg/mL.
• Infusions in Transport: dedicated pump channel and line; pump concentration must match the bag; enough volume for the trip; check the IV site after every move.
• Handoff Essentials: total bolus dose and times, current rate in mcg/min or mcg/kg/min (and the weight used), concentration, last titration and BP and heart rate response, other vasopressors, line type and site condition.

Mechanism of Action

• Selective α₁-adrenergic agonism → arterial and venous constriction → higher systemic vascular resistance, venous return and MAP.
• No meaningful β activity at clinical doses → no direct rise in heart rate or contractility.
• Baroreceptor reflex → increased vagal tone → reflex bradycardia. Cardiac output may fall, especially with LV dysfunction.
• Regional vasoconstriction in renal, splanchnic and hepatic beds → risk of organ ischemia at high doses.

Pharmacokinetics

• Half-life: the effective half-life, about 5 min, drives the clinical effect. The terminal elimination half-life is about 2.5 hr.
• Metabolism: monoamine oxidase (main pathway) and sulfotransferase.
• Active metabolites: none (m-hydroxymandelic acid about 57%, sulfate conjugates about 8%, both inactive).
• Elimination: about 86% recovered in urine within 48 hr, about 16% unchanged.
• Protein binding / Vd: Vd about 340 L (extensive tissue distribution); clearance about 2,100 mL/min.

Generic Name

Phenylephrine hydrochloride

Brand Names

Biorphen (US injection, 100 mcg/mL and 10 mg/mL); Immphentiv (US injection, 100 mcg/mL ready-to-use); generic vials and premixed bags. Neo-Synephrine was formerly also an injection brand and is now mainly an OTC nasal decongestant; Sudafed PE is an oral OTC decongestant

Pharmacologic Class

Selective α₁-adrenergic agonist (synthetic sympathomimetic amine, non-catecholamine)

Therapeutic Class

Vasopressor

Controlled Substance

Not controlled

ISMP High-Alert

Yes: ISMP high-alert medication (adrenergic agonists, IV)

Look-Alike / Sound-Alike

Concentration mix-up: 10 mg/mL concentrate vs 100 mcg/mL ready-to-use product (a 100-fold difference); keep them in separate bins