Metaraminol

Why this drug is interesting

Metaraminol is a curiously local drug. It is used routinely in UK and Australasian emergency departments, anaesthetic rooms and critical care units, and is largely unfamiliar to North American practice, where phenylephrine occupies the same niche. If you read international literature on vasopressors you will find very little about it.

Its appeal is practical rather than pharmacological: it can be given by peripheral bolus or infusion, which makes it the agent that bridges the gap between recognising shock and establishing central access. Its dual mechanism — direct α₁ agonism plus indirect release of stored noradrenaline — is what makes it effective and also what makes it fail over time.

Pharmacology

The dual mechanism

Metaraminol acts in two ways:

• Directly, as an agonist at α₁ adrenoceptors, producing arterial and venous vasoconstriction
• Indirectly, by being taken up into sympathetic nerve terminals and displacing stored noradrenaline into the synaptic cleft

It also means metaraminol may be less effective in patients with depleted catecholamine stores — chronic heart failure, prolonged shock, or those on drugs such as reserpine — where a purely direct agonist like noradrenaline or phenylephrine is more reliable.

Haemodynamic effects

Onset

Within 1–2 minutes intravenously

Duration

Roughly 20–60 minutes after a bolus — considerably longer than noradrenaline

Blood pressure

Rises through increased systemic vascular resistance

Heart rate

Falls — reflex bradycardia from baroreceptor activation

Cardiac output

May fall as afterload rises, particularly in the failing ventricle

Indications and dosing

Metaraminol is used for acute hypotension, most commonly the vasoplegia of anaesthesia and sedation, hypotension in sepsis while definitive access and support are arranged, and as an adjunct in other distributive shock states.

In refractory anaphylaxis

The RCUK refractory anaphylaxis algorithm lists metaraminol among the second vasopressors that may be added to an adrenaline infusion, alongside noradrenaline and vasopressin.³ See Adrenaline.

Peripheral administration

Metaraminol's routine peripheral use is its main practical advantage over noradrenaline. It is still a vasoconstrictor and extravasation can cause tissue injury — use a well-sited cannula in a large vein, inspect it regularly, and treat extravasation as for noradrenaline, with phentolamine infiltration. See Noradrenaline.

Contraindications, adverse effects and interactions

Cautions and contraindications

• Hypersensitivity to metaraminol
• Uncorrected hypovolaemia — as with any vasopressor, fill the circulation first
• Hypertension and significant cardiovascular disease
• Ischaemic heart disease — increased afterload and myocardial oxygen demand
• Hyperthyroidism
• Diabetes — may raise blood glucose and alter insulin requirements
• Cirrhosis and portal hypertension — caution
• Concurrent MAO inhibitors — see below
• Peripheral or mesenteric vascular thrombosis

Adverse effects

• Reflex bradycardia — expected and usually benign
• Hypertension, potentially severe and prolonged given the duration of action
• Peripheral and splanchnic ischaemia
• Arrhythmia; reduced cardiac output in the failing ventricle
• Extravasation injury
• Headache, anxiety, tremor, sweating
• Hyperglycaemia; abscess formation at injection sites with repeated use

Other interactions

• Volatile anaesthetics — myocardial sensitisation to catecholamine arrhythmia
• Beta-blockers — unopposed α effects, exaggerated hypertension
• Other vasopressors — additive ischaemic risk
• Ergot alkaloids and oxytocics — additive vasoconstriction

Critical appraisal

1. The evidence base is thin, and much thinner than its everyday use implies. Metaraminol's place in UK practice rests on familiarity, availability and convenience rather than on comparative outcome trials. There is very little randomised evidence comparing it against noradrenaline or phenylephrine on patient-centred outcomes.
2. Its geographical isolation is worth noticing. A drug used constantly in one healthcare system and essentially not at all in another is usually a sign that the choice is driven by habit and formulary rather than by evidence of superiority. That does not make it wrong — but it should temper confidence that it is the best available option.
3. Tachyphylaxis is often mistaken for clinical deterioration. A patient needing escalating metaraminol may be getting sicker, or may simply have depleted their noradrenaline stores. Distinguishing the two matters, because the responses differ — escalate care in the first case, switch agent in the second.
4. The convenience argument is genuinely strong, and should not be dismissed. Peripheral vasopressor support available within a minute in a resus room is worth a great deal compared with a theoretically superior agent that requires central access first. That said, noradrenaline is increasingly given peripherally too, which narrows metaraminol's main advantage.
5. It is a bridge, not a destination. A patient who still needs vasopressor support after the first hour needs a considered plan for definitive support and critical care review — not more metaraminol.

References

1. 1
   Metaraminol 10 mg/mL Solution for Injection or Infusion — Summary of Product Characteristics. electronic Medicines Compendium. Sections 4.2, 4.4. Verified 20 Aug 2026. A 0.5 mg/mL pre-filled syringe is also licensed — see emc.
2. 2
   Metaraminol — dosing and safety monograph. BNF, NICE. bnf.nice.org.uk
3. 3
   Resuscitation Council UK. Refractory anaphylaxis algorithm, 2021. resus.org.uk — mirrored at lifesupport.resusdoc.uk. Lists metaraminol among second vasopressors alongside noradrenaline and vasopressin.
4. 4
   Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock 2021. Crit Care Med 2021;49(11):e1063–143. Notable for what it does not contain — metaraminol does not feature in international vasopressor recommendations.
5. 5
   Owen VS, Rosgen BK, Cherak SJ, et al. Adverse events associated with administration of vasopressor medications through a peripheral intravenous catheter: a systematic review and meta-analysis. Crit Care 2021;25(1):146.