Clinical Disease

pharmacology

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Phenylephrine vs Norepinephrine: Choosing the Right Vasopressor

Pure α-agonist phenylephrine vs α + weak β1 norepinephrine for perioperative and obstetric hypotension

Phenylephrine (pure α-agonist) treats perioperative hypotension but causes dose-dependent reflex bradycardia and decreased CO; norepinephrine (α + weak β1) preserves HR and CO. Both are equally effective for cesarean spinal-induced hypotension with no difference in neonatal outcome.

If you forget

Pure α-agonists cause baroreflex bradycardia + decreased CO

Board trap

Patient on escalating phenylephrine develops bradycardia - that is an α-mediated baroreflex, NOT sepsis-induced bradycardia or vagal syncope. Correct response: reduce phenylephrine, switch to norepinephrine (β1 offsets the reflex), or add glycopyrrolate 0.2 mg IV - do NOT give more phenylephrine.

Key numbers

Phenylephrine 50-100 μg IV bolus (≈0.5-1 μg/kg), titrated q1-3 min
Phenylephrine fixed-rate infusion 50 μg/min for cesarean SAIH prophylaxis
Norepinephrine 5 μg/mL infusion; optimal initiation 0.07-0.08 μg/kg/min
Intraop MAP ≥60-65 mmHg; SBP ≥90 mmHg (organ-injury goal)

Reviewed Sep 24, 2026 for clinical accuracy by BoardsBridge Editorial Process

Uri Rozen, MD — Licensed Physician, Israel

Source guidelines: Ferre Spinal Hypotension Adults 2020 · Ferre Spinal Hypotension Adults 2020 · Ferre Spinal Hypotension Adults 2020 · AHA ACC Perioperative Cardiovascular 2024

Re-review cadence: 12 months from reviewed date.

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Card ID: phenylephrine-vs-norepi · Path: aba.pharmacology.vasopressors-and-inotropes.phenylephrine-vs-norepi