Inj Noradrenaline and Inj Dopamine mode of action and use
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norepinephrine AND dopamine
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Surviving Sepsis Campaign norepinephrine dopamine vasopressor recommendation
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1. Injection Noradrenaline (Norepinephrine)
Mode of action
Noradrenaline is a sympathomimetic catecholamine that acts mainly on:
- Alpha-1 receptors: powerful arterial and venous vasoconstriction
- Raises systemic vascular resistance (SVR)
- Raises blood pressure and mean arterial pressure (MAP)
- Alpha-2 receptors: reduces further norepinephrine release from nerve terminals
- Beta-1 receptors: mild increase in cardiac contractility
It has very little beta-2 activity. The rise in BP may produce reflex bradycardia, so heart rate may not increase despite beta-1 activity.
Main uses
- First-line vasopressor in septic shock after appropriate fluid resuscitation
- Acute severe hypotension due to vasodilatory shock, for example:
- Septic shock
- Neurogenic shock
- Anesthesia-related vasodilation
- Support of BP in critically ill patients while the underlying cause is treated
The Surviving Sepsis Campaign guideline recommends norepinephrine as the first-line vasopressor for adults with septic shock.
Important adverse effects / precautions
- Excess vasoconstriction can reduce perfusion to skin, kidneys, gut, and limbs
- Tachyarrhythmias are possible, though usually less frequent than with dopamine
- Extravasation can cause severe local ischemia and tissue necrosis
- Give as a titrated continuous IV infusion, preferably through a central venous catheter, with continuous BP and cardiac monitoring
2. Injection Dopamine
Mode of action
Dopamine is an endogenous catecholamine and a precursor of norepinephrine. Its receptor action is dose-dependent:
| Infusion range | Predominant receptor effects | Main effect |
|---|---|---|
| Low dose | Dopaminergic D1 receptors | Renal and splanchnic vasodilation |
| Moderate dose | Beta-1 receptors | Increased heart rate, contractility, and cardiac output |
| High dose | Alpha-1 receptors | Vasoconstriction and increased BP |
In practice, do not use low-dose dopamine merely to increase urine output or as “renal-dose dopamine.” It has not been shown to protect kidney function in critically ill patients.
Main uses
- Selected cases of hypotension with low cardiac output, particularly if there is significant bradycardia
- Cardiogenic shock in limited circumstances, especially when hypotension is present and an alternative is unsuitable
- Alternative vasopressor only when norepinephrine is unavailable or not appropriate
Dopamine was historically used in septic shock, but it causes more tachyarrhythmias than norepinephrine. Current sepsis guidance favors norepinephrine; dopamine is an alternative where norepinephrine is unavailable, with particular caution in patients at risk of arrhythmia. See the SCCM guideline summary.
Important adverse effects / precautions
- Tachycardia and arrhythmias, especially atrial fibrillation and ventricular arrhythmias
- Increased myocardial oxygen demand, which can worsen myocardial ischemia
- Nausea, headache, peripheral ischemia at high doses
- Extravasation can cause tissue necrosis
- Continuous ECG and BP monitoring are required
Quick comparison
| Feature | Noradrenaline | Dopamine |
|---|---|---|
| Main receptor action | Alpha-1 > beta-1 | Dose-dependent D1, beta-1, alpha-1 |
| Dominant clinical effect | Vasoconstriction, raises MAP | Raises cardiac output at moderate dose; vasoconstriction at high dose |
| Septic shock | Preferred first-line | Usually avoided if norepinephrine is available |
| Arrhythmia risk | Lower | Higher |
| Useful when | Vasodilatory hypotension | Hypotension with low output and marked bradycardia, selected cases |
Clinical note: These are high-risk ICU/emergency medicines. They must be administered as titrated infusions under trained supervision with monitoring and treatment of the cause of shock, not simply to normalize the BP.
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