Plasma Half-Life of Noradrenaline (Norepinephrine)
The plasma half-life of noradrenaline is approximately 1.5 to 2 minutes in humans under normal physiological conditions.
Pharmacokinetic Evidence
The most direct evidence comes from animal research that closely models human physiology. In freely moving rats, exogenous noradrenaline demonstrates a half-life of 1.5 minutes under normal conditions 1. When both neuronal and extra-neuronal uptake mechanisms are blocked pharmacologically, this extends to 6.3 minutes, demonstrating the critical role of active uptake systems in noradrenaline clearance 1.
Clinical Context
This extremely short half-life has important clinical implications:
- Rapid onset and offset: Noradrenaline's effects appear and disappear quickly, which is why continuous infusion is required for sustained hemodynamic support
- Titration flexibility: The brief half-life allows for rapid dose adjustments in critically ill patients, with hemodynamic changes occurring within minutes
- Metabolism pathway: The rapid clearance occurs through multiple mechanisms including neuronal reuptake (uptake-1), extra-neuronal uptake (uptake-2), and enzymatic degradation by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT)
Practical Implications
The 1.5-2 minute half-life explains why:
- Noradrenaline must be given as continuous infusion rather than bolus dosing
- Hemodynamic effects dissipate rapidly if infusion is interrupted
- Dose adjustments produce observable effects within 5-10 minutes (approximately 3-5 half-lives)
- Steady-state plasma concentrations are achieved within 7.5-10 minutes of starting or changing the infusion rate
This contrasts sharply with longer-acting vasopressors like vasopressin, whose active metabolite (OR1896 for levosimendan) can have half-lives measured in hours to days 2.