Ketamine Half-Life
The plasma elimination half-life of ketamine after intravenous administration in adults is approximately 2.5 hours (redistribution/beta phase), with an initial distribution half-life of 10-15 minutes (alpha phase). 1
Pharmacokinetic Profile
According to the FDA drug label, ketamine exhibits biphasic elimination kinetics following intravenous administration 1:
Distribution Phase (Alpha Phase)
- Half-life: 10-15 minutes
- Duration: approximately 45 minutes
- This phase corresponds clinically to the anesthetic effect of the drug
- Represents rapid redistribution from the CNS to peripheral tissues
Elimination Phase (Beta Phase)
- Half-life: 2.5 hours (150 minutes)
- Represents redistribution from CNS to slower equilibrating peripheral tissues combined with hepatic biotransformation to norketamine
- This is the terminal elimination half-life used for dosing calculations
Supporting Research Evidence
The research literature corroborates these FDA-established values, though with some variability:
- Studies in healthy volunteers report terminal half-lives ranging from 79-186 minutes 2, 3, 4
- A Japanese pharmacokinetic study found T½β of approximately 120 minutes 5
- Clinical anesthesia studies reported elimination half-lives of 60 minutes (beta phase) 6
Important Clinical Considerations
The initial 10-15 minute distribution half-life explains ketamine's rapid onset and offset of anesthetic effects, while the 2.5-hour elimination half-life is relevant for:
- Determining dosing intervals for repeated administration
- Predicting duration of systemic effects
- Understanding accumulation risk with continuous infusions
Metabolism: Ketamine is primarily metabolized to the active metabolite norketamine (approximately 1/3 as potent) via CYP2B6 and CYP3A4 1. This metabolite has its own pharmacologic activity and must be considered in clinical effects.
The FDA label values should be used for clinical decision-making, as they represent the authoritative pharmacokinetic parameters for dosing and safety monitoring.