Metaraminol

 Action Acts directly on alpha receptors, causing peripheral vasoconstriction. Increase in systolic, diastolic blood and pulmonary pressure results, as does increase in cardiac output.

 Indications Prevention and treatment of acute hypotensive state occurring with spinal anesthesia; adjunctive treatment of hypotension due to hemorrhage, reactions to medications, surgical complications and shock associated with brain damage due to trauma or tumor. Probably effective as adjunct in hypotension due to cardiogenic shock or septicemia.

 Contraindications Use with cyclopropane or halothane anesthesia unless essential.

 Route/Dosage

Prevention of Hypotension

ADULTS: SC/IM 2–10 mg; wait at least 10 min before readministering. CHILDREN: SC/IM 0.1 mg/kg.

Treatment of Hypotension

ADULTS: IV 15–100 mg in 250–500 ml of normal saline or D5W; adjust rate to response; ay concentrate further in fluid-restricted states. CHILDREN: SC/IM 0.1 mg/kg.

Treatment of Severe Shock

ADULTS: IV push 0.5–5 mg followed by infusion of 15–100 mg in 500 ml of normal saline or D5W. CHILDREN: IV 0.01 mg/kg as single dose or via infusion of 1 mg/25 ml in normal saline or D5W.

 Interactions

Guanethidine: Antihypertensive effects of guanethidine may be negated. MAO inhibitors, furazolidone, rauwolfia alkaloids, methyldopa: May significantly increase pressor response, possibly resulting in hypertensive crisis and intracranial hemorrhage. Tricyclic antidepressants: May decrease pressor response. INCOMPATIBILITIES: Metaraminol is incompatible with many drugs; consult reference prior to admixture.

 Lab Test Interferences None well documented.

 Adverse Reactions

CV: Sinus or ventricular tachycardia or other arrhythmias, especially in predisposed patients; hypertension or hypotension following cessation of drug; cardiac arrest; palpitations; flushing. CNS: Headaches; dizziness; apprehension. GI: Nausea. OTHER: Sweating; abscess formation; tissue necrosis; sloughing at injection site.

 Precautions

Pregnancy: Category C. Lactation: Undetermined. Extravasation: Avoid by infusing into large vein and monitoring carefully. Sulfite sensitivity: Use caution in sulfite-sensitive individuals; some preparations contain sodium bisulfite.

 Administration/Storage

• Dilute in normal saline or D5W. Use large veins to decrease irritation and/or tissue necrosis at parenteral administration sites. If given directly IV, follow with infusion to decrease possibility of necrosis.
• After administration, observe patient for effects before repeating dose. Pressor effects occur 1–2 min after IV dose, 10 min after IM dose, and 5–20 min after SC dose.
• Avoid IM injection to prevent tissue sloughing at injection site.
• Use infusion solutions within 24 hrs of mixing.
• Avoid exposing drug to excessive heat. Protect from light.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Monitor cardiac status, BP, pulse and respiration rate frequently, especially with IV administration. Fall in BP may occur with repeated use of metaraminol. Check BP every 5 min until stabilized and then check every 5 min throughout therapy.
• Notify physician if significant changes or arrhythmias occur.
• Monitor I&O.
• Monitor patient for sympathomimetic side effects such as: izziness, headaches, restlessness, faintness, anxiety, flushing and apprehension.
• Monitor for hypertensive crisis and intracranial hemorrhage if given with MAO inhibitors, furazolidone, rauwolfia alkaloids and methyldopa.
• Observe for metabolic acidosis with prolonged use.
• When infusion is to be discontinued, gradually reduce flow rate.
• Document any side effects or adverse reactions, including arrhythmias, hypertension or hypotension after stopping drug, cardiac arrest and nausea.

 Patient/Family Education

• Alert patient to the possible problems of extravasation. Instruct patient to report symptoms such as paresthesia, respiratory distress, chest pain, palpitations or irritation or pain at injection site.
• Educate patient and family regarding sympathomimetic side effects.