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Action/Kinetics:
Acts indirectly by releasing norepinephrine from its storage sites and directly by exerting a slight effect on alpha and beta-1 receptors and a moderate effect on beta-2 receptors mediating vasodilation. Causes increased CO; also elicits slight CNS effects.
IV: Onset, immediate;
duration: 15-30 min.
IM: Onset, 5-15 min;
duration: 1-2 hr. Metabolized in liver. Excreted in urine within 24 hr (rate increased in acidic urine).
Uses:
Hypotension due to anesthesia, ganglionic blockade, or hemorrhage (only as emergency treatment until blood or blood substitutes can be given).
Contraindications:
To treat hypotension caused by chlorpromazine. In combination with MAO inhibitors.
Special Concerns:
Use with caution in CV disease, in chronically ill clients, and in treating shock secondary to hemorrhage. Safety and efficacy have not been demonstrated in children.
Side Effects:
Anxiety, cardiac arrhythmias, increased BP (especially in those with heart disease).
Additional Drug Interactions:
Mephentermine will potentiate hypotensive effects of phenothiazines.
How Supplied:
Injection: 15 mg/mL, 30 mg/mL
Dosage
?IV, IM
Hypotension during spinal anesthesia.
IV, Adults: 30-45 mg; 30-mg doses may be repeated as required; or,
IV infusion, Adults and children: 0.1% (1 mg/mL) mephentermine in D5W with the rate of infusion and duration dependent on client response.
IV, Pediatric: 0.4 mg/kg (12 mg/m
2) as a single dose.
Prophylaxis of hypotension in spinal anesthesia.
IM, Adults: 30-45 mg 10-20 min before anesthesia.
IM, Pediatric: 0.4 mg/kg (12 mg/m
2) as a single dose.
Shock following hemorrhage.
Not recommended, but IV infusion of 0.1% in D5W may maintain BP until blood volume is replaced.
