Ketamine is an NMDA-antagonist dissociative anesthetic and analgesic, increasingly used therapeutically at subanesthetic doses for neuropathic pain and treatment-resistant depression, and also used illicitly for its dissociative effects. LC-MS/MS measures ketamine and its active metabolite norketamine, which often exceeds the parent and extends the detection window.1
Renewed clinical use of ketamine for depression and pain means a positive result increasingly reflects legitimate therapy, not only illicit use, so interpretation requires the clinical context. Illicit use persists, primarily among young adults, for its hallucinogenic effects.2
Ketamine is not on standard immunoassay panels; targeted LC-MS/MS measures ketamine and norketamine. Because norketamine often exceeds ketamine and persists longer, measuring both improves detection.3 Ordering may confirm ketamine presence, verify complete elimination before a new therapy, or check for illicit use.1
Confirms recent exposure. Ketamine and/or norketamine indicates use within roughly 2 to 3 days.
Does not distinguish source. Medical and illicit ketamine are not differentiated by the assay.
Norketamine extends the window. The metabolite often exceeds the parent and persists longer.3
Short parent half-life. Ketamine clears quickly (half-life ~2 to 3 h); a negative may reflect timing.
Not on routine panels. Standard screens do not include ketamine.
Timing and cutoff. Absence may reflect timing of last use or levels below the cutoff.
Ketamine analytes measured on definitive testing.
| Metabolite | Clinical Significance |
|---|---|
| Ketamine (parent) | Short half-life (~2 to 3 h); NMDA antagonist. |
| Norketamine | Active metabolite; often exceeds parent and extends the window. |