The following reactions can occur: Body as a whole: Ischaemic injury due to potent vasoconstrictor action and tissue hypoxia.
Cardiovascular System: Bradycardia, probably as a reflex result of a rise in blood pressure, arrhythmias.
Nervous System: Anxiety, transient headache.
Respiratory System: Respiratory difficulty.
Skin and Appendages: Extravasation necrosis at injection site.
Prolonged administration of any potent vasopressor may result in plasma volume depletion which should be continuously corrected by appropriate fluid and electrolyte replacement therapy. If plasma volumes are not corrected, hypotension may recur when norepinephrine is discontinued, or blood pressure may be maintained at the risk of severe peripheral and visceral vasoconstriction (eg, decreased renal perfusion) with diminution in blood flow and tissue perfusion with subsequent tissue hypoxia and lactic acidosis and possible ischaemic injury. Gangrene of extremities has been rarely reported. Overdoses or conventional doses in hypersensitive persons (eg, hyperthyroid patients) cause severe hypertension with violent headache, photophobia, stabbing retrosternal pain, pallor, intense sweating and vomiting.