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# Norepinephrine
## Overview
Norepinephrine is a potent alpha-1 adrenergic agonist and a weaker beta-1 adrenergic agonist. It causes peripheral vasoconstriction, leading to increased systemic vascular resistance and blood pressure. It also has some inotropic and chronotropic effects on the heart.
## Primary Indications
* Treatment of hypotension and shock, particularly in septic shock and vasodilatory shock.
* Restoration and maintenance of blood pressure.
## Adult Dosing
* **Initial dose:** 0.01 to 0.02 mcg/kg/min IV.
* **Titration:** Titrate infusion rate based on patient's hemodynamic response (e.g., mean arterial pressure [MAP]). Doses can be increased in increments of 0.01 to 0.02 mcg/kg/min every 5-15 minutes.
* **Maximum dose:** Typically 0.3 mcg/kg/min IV, though higher doses may be used in refractory hypotension under close monitoring.
## Pediatric Dosing
* **Initial dose:** 0.05 mcg/kg/min IV.
* **Titration:** Titrate infusion rate based on patient's hemodynamic response. Doses can be increased in increments of 0.05 to 0.2 mcg/kg/min every 5-15 minutes.
* **Maximum dose:** Typically 1 mcg/kg/min IV, though higher doses may be used under close monitoring.
* *Note: Dosing can vary significantly based on the specific clinical scenario and institutional protocols.*
## Dose Adjustments
* No dose adjustment is typically required for renal or hepatic impairment, but close monitoring of hemodynamic response is crucial as metabolism and excretion can be affected.
## Contraindications
* Hypersensitivity to norepinephrine.
* Hypotension due to absolute hypovolemia unless used as a temporizing measure while definitive volume replacement is being initiated.
* During general anesthesia with cyclopropane or halogenated hydrocarbons, as these can sensitize the myocardium to catecholamines.
## Adverse Effects
* **Cardiovascular:** Arrhythmias (tachycardia, bradycardia, ventricular fibrillation), hypertension, peripheral ischemia, extravasation leading to tissue necrosis, palpitations, angina.
* **Central Nervous System:** Headache, anxiety, dizziness, tremor.
* **Other:** Dyspnea, nausea, vomiting, decreased urine output.
## Key Drug Interactions
* **Monoamine Oxidase Inhibitors (MAOIs) and Tricyclic Antidepressants (TCAs):** Potentiate the pressor response and may cause hypertensive crisis. Avoid concurrent use or use with extreme caution and significantly reduced doses.
* **Alpha-adrenergic Blockers (e.g., prazosin):** May antagonize the pressor effects of norepinephrine.
* **Beta-adrenergic Blockers:** May block the beta-1 effects of norepinephrine, potentially leading to unopposed alpha-1 mediated vasoconstriction and severe hypertension.
* **Ergot alkaloids, oxytocics:** May cause severe persistent hypertension.
* **Anesthetics (e.g., halothane, isoflurane):** Increased risk of arrhythmias.
## Monitoring
* **Hemodynamic parameters:** Continuous monitoring of blood pressure (MAP), heart rate, and rhythm is essential.
* **Central venous pressure (CVP) and pulmonary artery pressures (if available):** To guide fluid management.
* **Urine output:** To assess perfusion.
* **Peripheral circulation:** Monitor for signs of ischemia (e.g., coolness, color changes, pain) in extremities, especially with prolonged use or high doses.
* **Infusion site:** For signs of extravasation.
## Clinical Pearls
* Always administer norepinephrine via a central venous catheter to minimize the risk of extravasation and tissue necrosis.
* If extravasation occurs, stop the infusion immediately and infiltrate the affected area with phentolamine (an alpha-adrenergic blocker).
* Norepinephrine is often the first-line vasopressor in septic shock.
* Titrate to the lowest effective dose to achieve the desired hemodynamic goal (e.g., MAP > 65 mmHg).
* Be aware of the potential for reflex bradycardia.
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*This information is intended for healthcare professionals and does not replace a thorough review of the official prescribing information or consultation with a pharmacist. Always verify current prescribing information before making clinical decisions.*
