Mephentermine Sulfate

 Action Acts directly and indirectly (via release of norepinephrine) on beta and alpha receptors, causing increase in cardiac contraction and, to lesser degree, increase in peripheral vasoconstriction.

 Indications Treatment of hypotension secondary to ganglionic blockade and to spinal anesthesia; maintenance of blood pressure until blood or blood substitutes may be administered during hypovolemic shock.

 Contraindications Hypotension induced by chlorpromazine; use of MAO inhibitors.

 Route/Dosage

Shock and Hypotension

ADULTS: IM 0.5 mg/kg undiluted. IV 1 mg/ml solution in D5W titrated to clinical response.

Hypotension Following Spinal Anesthesia

ADULTS: IV 30–45 mg; repeat doses of 30 mg prn; or give as 1 mg/ml infusion in D5W titrated to clinical response.

Prevention of Hypotension Following Spinal Anesthesia

ADULTS: IM 30–45 mg 10–20 min prior to anesthesia, operation or termination of operative procedure.

Hypotension Secondary to Spinal Anesthesia During Cesarean Section

ADULTS: IV 15 mg; repeat prn.

Hemorrhagic Shock

ADULTS: IV Continuous infusion of 1 mg/ml solution in D5W until whole blood replacement can be accomplished.

 Interactions

Guanethidine: Antihypertensive effects of guanethidine may be negated. Halogenated hydrocarbon anesthetics: May sensitize myocardium to arrhythmogenic effects of catecholamines. MAO inhibitors, furazolidone, rauwolfia alkaloids, methyldopa: May significantly increase pressor response, possibly resulting in hypertensive crisis and intracranial hemorrhage. Oxytoxic drugs: Synergistic or additive vasoconstrictive effects may occur, resulting in hypertension and possible gangrene in the extremities. Tricyclic antidepressants: May decrease pressor response.

 Lab Test Interferences None well documented.

 Adverse Reactions

CV: Cardiac arrhythmias; excessive hypertension, especially in patients with heart disease. CNS: Anxiety; seizures.

 Precautions

Pregnancy: Category C. Lactation: Undetermined. Cardiovascular effects: May be profound. Use with caution in chronically ill patients and patients with known cardiovascular disease or hyperthyroidism. Hypovolemia: Avoid in patients with uncorrected hypovolemia. Persistent hypotension may indicate hypovolemia.

 Administration/Storage

• If solution is discolored, do not use; discard.
• IV solution can be prepared by adding 10 or 20 ml of 30 mg/ml mephentermine to 250 ml or 500 ml of D5W, respectively.
• Store reconstituted solution no longer than 24 hr.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Use electronic infusion device for IV administration.
• Monitor I&O. If urinary output is < 30 ml/hr, notify physician.
• Monitor BP during IV administration and every 5 min after IM administration.

 Patient/Family Education

• Instruct patient and family to notify physician if any otc cold or allergy preparation has been used within 3 days of surgery.
• Inform physician of use of MAO inhibitors or tricyclic antidepressants within 1 mo of surgery.