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# Norepinephrine
## Overview
Norepinephrine is a potent alpha-1 adrenergic agonist and a weaker beta-1 adrenergic agonist. It causes vasoconstriction, leading to increased peripheral vascular resistance and blood pressure. Beta-1 agonism can increase heart rate and contractility, but this effect is often blunted by reflex bradycardia.
## Primary Indications
* Treatment of hypotension, particularly in septic shock and other distributive shock states, to maintain adequate mean arterial pressure (MAP).
* Cardiogenic shock.
## Adult Dosing
* **Intravenous infusion:** Typically initiated at 0.01 to 0.05 mcg/kg/min, titrated to achieve target MAP (often $\ge$ 65 mmHg). Doses can be increased up to 0.1 to 0.4 mcg/kg/min, and in some cases, higher doses (up to 2 mcg/kg/min) may be necessary. The exact initial dose and titration range are often dictated by institutional protocols.
## Pediatric Dosing
* **Intravenous infusion:** Typically initiated at 0.05 to 0.1 mcg/kg/min, titrated to achieve target MAP (often $\ge$ age in years + 20 mmHg, or $\ge$ 50 mmHg). Doses can be increased up to 1 mcg/kg/min, and in refractory cases, up to 2 mcg/kg/min. The exact initial dose and titration range are often dictated by institutional protocols.
## Dose Adjustments
No specific dose adjustments are generally required for renal or hepatic impairment, as norepinephrine is metabolized extrahepatically. However, titrate cautiously in patients with compromised organ perfusion due to potential for further vasoconstriction.
## Contraindications
* Hypersensitivity to norepinephrine.
* Should not be used as the primary agent in hypotensive patients with mechanical obstruction to blood flow (e.g., tension pneumothorax, cardiac tamponade).
* Use with extreme caution in patients with occlusive vascular disease (e.g., peripheral vascular disease, cold extremities) due to the risk of exacerbating ischemia.
## Adverse Effects
* **Cardiovascular:** Hypertensive crisis, reflex bradycardia, arrhythmias, chest pain, peripheral ischemia (due to vasoconstriction), gangrene (with prolonged extravasation or high doses).
* **Other:** Anxiety, headache, dizziness, tremors, nausea, vomiting, dyspnea, urinary retention.
## Key Drug Interactions
* **General anesthetics:** May potentiate arrhythmias.
* **Beta-adrenergic blocking agents:** May cause unopposed alpha-adrenergic stimulation leading to severe hypertension.
* **MAO inhibitors and tricyclic antidepressants:** Can prolong and intensify the pressor effects of norepinephrine. Discontinue MAO inhibitors at least 14 days prior to initiating norepinephrine.
* **Ergot alkaloids:** May cause severe hypertension.
* **Oxytocics:** May cause severe hypertension.
* **Alpha-adrenergic blocking agents:** May reduce the pressor effect.
## Monitoring
* Continuous blood pressure monitoring (intra-arterial preferred for precise titration).
* Heart rate and rhythm.
* Urine output.
* Peripheral perfusion (e.g., skin color, temperature, capillary refill).
* Central venous pressure and pulmonary artery pressures (if available).
* Acid-base status and lactate levels in shock states.
## Clinical Pearls
* Norepinephrine should be administered via a central venous catheter to minimize the risk of extravasation and local tissue necrosis.
* If extravasation occurs, discontinue the infusion immediately and infiltrate the affected area with phentolamine (an alpha-adrenergic blocker) to counteract the vasoconstriction.
* Norepinephrine is typically mixed in dextrose 5% in water or normal saline. Avoid lactated Ringer's solution, as lactate may degrade norepinephrine.
* It is a potent vasopressor and should be used cautiously in patients with underlying ischemic conditions.
* Titrate to the lowest effective dose to achieve the target MAP and wean as soon as hemodynamics allow.
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*This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the current prescribing information and institutional protocols for complete and up-to-date guidance.*
