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## Norepinephrine
### Overview
Norepinephrine is a vasopressor and inotropic agent that acts primarily on alpha-1 adrenergic receptors, causing vasoconstriction and increasing peripheral vascular resistance. It also has some beta-1 adrenergic receptor activity, increasing heart rate and contractility.
### Primary Indications
* Treatment of severe hypotension and shock (e.g., septic shock, cardiogenic shock) unresponsive to adequate fluid resuscitation.
* Restoration and maintenance of blood pressure.
### Adult Dosing
* **Usual Dose:** 2 to 12 mcg/minute (0.01 to 0.06 mcg/kg/minute) IV infusion.
* **Initiation:** Typically started at 4 mcg/minute (0.02 mcg/kg/minute).
* **Titration:** Titrated to achieve target mean arterial pressure (MAP), often 65 mmHg or higher, or to reverse signs of hypoperfusion.
* **Maximum Dose:** Doses higher than 30 mcg/minute (0.2 mcg/kg/minute) are generally not recommended due to increased risk of adverse events.
### Pediatric Dosing
* **Usual Dose:** 0.05 to 2 mcg/kg/minute IV infusion.
* **Initiation:** Often started at 0.05 to 0.1 mcg/kg/minute.
* **Titration:** Titrated to achieve target MAP based on age (e.g., MAP > gestational age in weeks for neonates, MAP > 50 mmHg for infants/children).
* **Maximum Dose:** Individual protocols vary; consult institutional guidelines.
### Dose Adjustments
* **Fluid Resuscitation:** Norepinephrine should be used in conjunction with, not as a replacement for, adequate fluid resuscitation.
* **Renal or Hepatic Impairment:** No specific dose adjustments are typically necessary, but close monitoring for efficacy and toxicity is recommended as metabolism and clearance may be altered.
### Contraindications
* Hypersensitivity to norepinephrine.
* Use during general anesthesia with volatile hydrocarbons or halogenated ethers (risk of ventricular arrhythmias).
* Hypotension due to relative hypovolemia unless used as a temporizing measure pending volume replacement.
### Adverse Effects
* **Cardiovascular:** Hypertension, bradycardia (reflex), tachycardia, arrhythmias, peripheral ischemia, extravasation leading to tissue necrosis.
* **Other:** Headache, anxiety, tremor, dizziness, dyspnea, nausea, vomiting.
### Key Drug Interactions
* **Monoamine Oxidase Inhibitors (MAOIs) / Tricyclic Antidepressants (TCAs) / Cocaine / Anesthetics (volatile):** Potentiate hypertensive effects and risk of arrhythmias. Avoid concurrent use or use with extreme caution and lower initial doses.
* **Alpha-blockers (e.g., prazosin):** May decrease the pressor effect.
* **Beta-blockers (e.g., propranolol):** May potentiate unopposed alpha-receptor stimulation leading to severe hypertension and reflex bradycardia.
* **Ergot Alkaloids / Oxytocin:** Potentiate vasoconstriction.
* **Diuretics:** May potentiate hypotensive effects.
### Monitoring
* **Hemodynamics:** Continuous ECG, heart rate, blood pressure (arterial line preferred for continuous infusion).
* **Perfusion:** Urine output, capillary refill, mental status, lactate levels.
* **Infusion Site:** Closely monitor for signs of extravasation.
### Clinical Pearls
* Administer via a central venous catheter whenever possible to minimize risk of extravasation.
* If extravasation occurs, discontinue infusion immediately, do not disturb the area, and infiltrate the affected site with phentolamine mesylate.
* Norepinephrine has a short half-life; effects diminish rapidly upon discontinuation.
* Titrate to effect, not to a specific dose.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the official prescribing information and institutional protocols for complete details and to verify accuracy before making clinical decisions.
