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Pharmacotherapeutic group: Adrenergic and dopaminergic agents. ATC code: C01CA03.
Pharmacodynamics: Norepinephrine bitartrate functions as a peripheral vasoconstrictor (alpha-adrenergic action) and as an inotropic stimulator of the heart and dilator of coronary arteries (beta-adrenergic action).
The vascular effects of noradrenaline (norepinephrine) 1:1000 in the doses usually used clinically result from the simultaneous stimulation of alpha and beta adrenergic receptors in the heart and vascular system. Except in the heart, its action is predominantly on the alpha receptors. This results in an increase in the force (and in the absence of vagal inhibition) in the rate of myocardial contraction. Peripheral resistance increases and diastolic and systolic pressures are raised.
Pharmacokinetics: Absorption: Norepinephrine is ineffective orally, and subcutaneous absorption is poor. As a result, it is recommended that norepinephrine be administered only via the intravenous route. Following IV administration, the onset of activity is rapid, with a short duration of only 1 - 2 minutes after the infusion is discontinued.
Distribution: Norepinephrine localizes mainly in sympathetic nervous tissue. The drug crosses the placenta but not the blood-brain barrier.
Elimination: The pharmacologic actions of norepinephrine are terminated primarily by uptake and metabolism in sympathetic nerve endings. The drug is metabolized in the liver and other tissues by a combination of reactions involving the enzymes catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). The major metabolites are normetanephrine and 3-methoxy-4-hydroxy mandelic acid (vanillylmandelic acid, VMA), both of which are inactive. Other inactive metabolites include 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxymandelic acid, and 3,4-dihydroxyphenylglycol. Norepinephrine metabolites are excreted in urine primarily as the sulfate conjugates and, to a lesser extent, as the glucuronide conjugates. Only small quantities of norepinephrine are excreted unchanged.
