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Action/Kinetics:
Indirectly releases norepinephrine from storage sites and directly stimulates primarily alpha receptors and, to a slight extent, beta-1 receptors. Causes marked increases in BP due primarily to vasoconstriction and to a slight increase in CO. Reflex bradycardia is also manifested. Increases venous tone, causes pulmonary vasoconstriction, and increases pulmonary pressure, even if CO is decreased. CNS stimulation usually does not occur.
Onset: IV: 1-2 min;
IM: 10 min;
SC: 5-20 min.
Duration, IV: 20 min;
IM, SC: About 60 min. Metabolized in the liver and excreted through the urine and feces. Enhance urinary excretion of unchanged drug by acidifying the urine.
Uses:
Hypotension associated with surgery, spinal anesthesia, hemorrhage, trauma, infections, tumors, and adverse drug reactions. Adjunct to the treatment of either septicemia or cardiogenic shock.
Investigational: Injected intracavernosally to treat priapism due to phentolamine, papaverine, or other causes.
Contraindications:
Use with cyclopropane or halothane anesthesia (unless clinical conditions mandate such use). As a substitute for blood or fluid replacement.
Special Concerns:
Use with caution in cirrhosis, malaria, heart or thyroid disease, hypertension, diabetes, or during lactation. Hypertension and ischemic ECG changes may occur when used to treat priapism. Use is not a substitute for the replacement of blood, plasma, fluids, and electrolytes.
Additional Side Effects:
Rapidly induced hypertension may cause acute pulmonary edema, arrhythmias, and
cardiac arrest. Due to its long duration of action, cumulative effects are possible with prolonged increases in BP.
Drug Interactions:
-
Digitalis glycosides /
Risk of ectopic arrhythmias
-
Furazolidone / Possible hypertensive crisis and IC hemorrhage
-
Guanethidine / Antihypertensive drug effects may be partially or totally reversed
-
Halogenated hydrocarbons / Sensitization of the heart to catecholamines; use of metaraminol may cause serious arrhythmias
-
MAO Inhibitors / Possible hypertensive crisis and IC hemorrhage
-
Oxytocic drugs / Possiblity of severe, persistent hypertension
-
Tricyclic antidepressants /
Pressor effect of metaraminol
How Supplied:
Injection: 10 mg/mL
Dosage
?IM, SC
Prophylaxis of hypotension.
Adults: 2-10 mg given IM or SC;
pediatric: 0.01 mg/kg (3 mg/m
2) IM or SC.
?IV Infusion
Hypotension.
Adults: 15-100 mg in 250-500 mL of 0.9% NaCl injection or 5% dextrose injection by IV infusion at a rate to maintain desired BP (up to 500 mg/500 mL has been used).
Pediatric: 0.4 mg/kg (12 mg/m
2) by IV infusion in a solution containing 1 mg/25 mL 0.9% NaCl injection or 5% dextrose injection.
?Direct IV
Severe shock.
Adults: 0.5-5.0 mg by direct IV followed by IV infusion of 15-100 mg in 250-500 mL fluid.
Pediatric: 0.01 mg/kg (0.3 mg/m
2) by direct IV.
?Endotracheal Tube
If IV access is not possible, metaraminol may be given by an ET tube. Perform five quick insufflations; forcefully expel 5 mg diluted to 10 mL into the ET tube and follow with five quick insufflations.
