indication

For the treatment and prevention of hypotension due to hemorrhage, spinal anesthesia, and shock associated with brain damage

pharmacology

Metaraminol is a potent sympathomimetic amine that increases both systolic and diastolic blood pressure. Metaraminol is indicated for prevention and treatment of the acute hypotensive state occurring with spinal anesthesia. It is also indicated as adjunctive treatment of hypotension due to hemorrhage, reactions to medications, surgical complications, and shock associated with brain damage due to trauma or tumor. Metaraminol acts on both α1-adrenergic receptors but appears to have no effect on β-adrenergic receptors. It acts by increasing the force of the heart's pumping action as well as constricting peripheral blood vessels.

mechanism of action

Metaraminol acts through peripheral vasoconstriction by acting as a pure alpha-1 adrenergic receptor agonist, consequently increasing systemic blood pressure (both systolic & diastolic). Its effect is thought to be associated with the inhibition of adenyl cyclase which leads to an inhibition of the production of cAMP. Another effect of Metaraminol is that it releases norepinephrine from its storage sites indirectly.

toxicity

LD₅₀=240 mg/kg (rat, oral); LD₅₀=99 mg/kg (mouse, oral)

biotransformation

Hepatic

absorption

The effect starts 1-2 min after IV injection, 10 min after IM injection, 5-20 min after subcutaneous injection.

drug interactions

Amitriptyline: The tricyclic antidepressant, amitriptyline, increases the sympathomimetic effect of metaraminol.

Amoxapine: The tricyclic antidepressant, amoxapine, increases the sympathomimetic effect of metaraminol.

Clomipramine: The tricyclic antidepressant, clomipramine, increases the sympathomimetic effect of metaraminol.

Desipramine: The tricyclic antidepressant, desipramine, increases the sympathomimetic effect of metaraminol.

Doxepin: The tricyclic antidepressant, doxepin, increases the sympathomimetic effect of metaraminol.

Guanethidine: Metaraminol may decrease the effect of guanethidine.

Imipramine: The tricyclic antidepressant, imipramine, increases the sympathomimetic effect of metaraminol.

Isocarboxazid: Increased arterial pressure

Linezolid: Possible increase of arterial pressure

Methyldopa: Increased arterial pressure

Midodrine: Increased arterial pressure

Moclobemide: Moclobemide increases the sympathomimetic effect of metaraminol.

Nortriptyline: The tricyclic antidepressant, nortriptyline, increases the sympathomimetic effect of metaraminol.

Phenelzine: Increased arterial pressure

Rasagiline: Increased arterial pressure

Reserpine: Increased arterial pressure