Esketamine

Primary psychoactive pharmacology for esketamine is dominated by non-competitive antagonism at the N-methyl-D-aspartate (NMDA) receptor. Esketamine is the S(+)-enantiomer of ketamine and shows higher affinity at the NMDA receptor binding site than arketamine (R(-)-ketamine), a stereochemical difference often described as translating into higher anaesthetic and analgesic potency and helping to explain why esketamine was advanced as a distinct medicinal product. citeturn20view1turn13view1

The antidepressant mechanism is not established. A widely supported working model, derived largely from ketamine research, proposes that transient NMDA receptor blockade—especially on inhibitory interneurons—produces short-lived disinhibition and a glutamatergic surge, which increases AMPA receptor throughput and triggers synaptic-plasticity programmes (including BDNF-linked and mTOR-linked signalling). These downstream changes are hypothesised to reverse stress-associated synaptic deficits in prefrontal–limbic circuits and thereby produce symptom relief that can outlast acute intoxication. citeturn22search24turn10search29turn13view1

Esketamine is not pharmacologically ‘single-target’. Policy syntheses and mechanistic reviews emphasise actions beyond NMDA receptor antagonism, including measurable affinity for the mu-opioid receptor and interactions with monoamine transporters and other receptor systems. The extent to which these non-NMDA actions contribute to antidepressant response in humans is unresolved; they are, however, plausible contributors to the acute dissociative state, autonomic effects, and reinforcement liability that drive the need for controlled delivery. citeturn13view1turn10search29turn23search2

For intranasal administration, pharmacokinetics are specified in regulatory labelling. Absolute bioavailability is approximately 48%, with peak plasma concentrations typically reached 20–40 minutes after the last spray; the FDA label notes this timing corresponds to Cmax for monitoring purposes. Exposure increases are slightly more than dose-proportional across 28 mg, 56 mg and 84 mg. Esketamine is moderately protein bound (approximately 43%–45%), has a large apparent volume of distribution, and exhibits a terminal half-life of roughly 7–12 hours, supporting intermittent dosing rather than daily self-administration. citeturn8view2turn7view0turn31view3

Metabolism is largely hepatic. Esketamine is mainly metabolised via CYP2B6 and CYP3A4, with additional contribution from CYP2C9 and CYP2C19, through N-demethylation to noresketamine followed by hydroxylation and conjugation to multiple metabolites. The major circulating metabolite noresketamine is described as less potent at the NMDA receptor than the parent compound, and less than 1% of dose is excreted unchanged in urine. In clinical terms, meaningful psychoactive exposure is concentrated in the early post-dose window rather than being driven by slow conversion to long-lived active metabolites. citeturn7view0turn8view2

Route, administration context and dose–response are inseparable for esketamine’s psychiatric use. Each intranasal device delivers 28 mg across two sprays; a typical treatment session therefore delivers 56 mg (two devices) or 84 mg (three devices). In EU product information, TRD treatment begins with an induction phase (56 mg on day 1, then 56 mg or 84 mg twice weekly for weeks 1–4) followed by reduced-frequency maintenance tailored to the lowest frequency that maintains response; for psychiatric emergency due to MDD, the EU label specifies a short, intensive 4-week course at 84 mg twice weekly with dose reduction to 56 mg based on tolerability. These schedules co-evolved with monitoring requirements because the acute dissociative and haemodynamic effects are dose-related and temporally clustered after dosing. citeturn20view0turn31view4turn31view3

Biomarker and neuroimaging findings remain more mature for intravenous racemic ketamine than for intranasal esketamine, but the mechanistic hypothesis space overlaps. Neuroimaging studies with ketamine in depression implicate rapid shifts in fronto-limbic processing and large-scale network dynamics as candidate mediators of symptom change; contemporary syntheses argue that these systems-level effects offer the most plausible bridge between receptor pharmacology and clinical outcomes. It remains unclear which biomarker signatures (molecular, electrophysiological, or network-level) will generalise robustly enough to guide esketamine patient selection or dosing frequency in routine care. citeturn10search33turn8search0turn8search3turn22search24

Esketamine’s modern psychiatric story sits on top of ketamine’s longer trajectory. Ketamine was synthesised in the early 1960s as a phencyclidine-related arylcyclohexylamine intended to preserve anaesthesia while reducing the prolonged delirium of PCP, and it became widely used in human and veterinary medicine as a dissociative anaesthetic. Contemporary policy reviews continue to frame ketamine (and its enantiomers) as clinically valuable but also subject to substantial harms under chronic high-dose non-medical use. citeturn11search0turn11search3turn13view1

In the United States, ketamine (including its salts and isomers) was placed into Schedule III of the Controlled Substances Act in 1999, reflecting recognised medical uses alongside misuse liability; this legal status shaped subsequent clinical research by requiring controlled-substance handling without imposing the near-total restrictions associated with Schedule I. citeturn21search7turn21search11

The antidepressant renaissance began with small, controlled human studies of sub-anaesthetic ketamine showing rapid symptom improvement in depression. Early clinical reports (for example, Berman and colleagues, 2000, and later Zarate and colleagues at the US National Institute of Mental Health in 2006) catalysed two parallel lines of work: mechanistic exploration of glutamatergic and synaptic-plasticity pathways, and translational efforts to develop products and service models capable of delivering ketamine-class treatments safely and reproducibly. citeturn11search6turn11search7turn22search24

Esketamine emerged as the most commercially tractable enantiomer to pursue within a regulated pharmaceutical framework, in part because stereoselective differences in NMDA receptor affinity and potency provided a plausible rationale for dose optimisation and because intranasal delivery offered a practical outpatient route. Janssen’s development programme received FDA Breakthrough Therapy Designation for TRD in November 2013 and a second Breakthrough Therapy Designation for major depressive disorder with imminent risk for suicide in August 2016, reflecting preliminary evidence of rapid antidepressant and anti-suicidal-symptom effects. citeturn35search0turn35search2

Methodological sophistication has advanced markedly across the subsequent decade. Esketamine programmes evolved from short-term symptom-change endpoints to include relapse-prevention (randomised withdrawal) designs, long-term open-label exposure datasets, and tightly specified risk-minimisation systems. By 2025, the US label had expanded to allow TRD monotherapy, a notable regulatory shift that may reduce friction for some patients and address real-world discontinuation driven by tolerability or preference regarding concomitant oral antidepressants. citeturn5view3turn20view6turn34view3

Across controlled trials, the acute tolerability profile of intranasal esketamine is characterised by time-limited neuropsychiatric and autonomic effects that are most prominent in the first hours after dosing. For TRD, adverse reactions occurring at ≥2% and more frequently than placebo included nausea (25% vs 8%), vomiting (7% vs <1%), feeling drunk (7% vs <1%) and blood pressure increased (5% vs 2%), alongside vestibular and perceptual symptoms such as vertigo. In the MDD with acute suicidal ideation or behaviour programme, dissociation (48% vs 13%), dizziness (45% vs 15%), sedation (29% vs 12%) and blood pressure increased (15% vs 6%) were prominent. These effects commonly peak near Cmax and are the immediate reason the product is delivered only in supervised healthcare settings. citeturn31view4turn34view1turn20view0

Cardiovascular and cerebrovascular risk management is central. Esketamine can cause clinically meaningful increases in blood pressure; the FDA label recommends reassessment at approximately 40 minutes post-dose (corresponding with Cmax) and continued monitoring until values decline, with emergency evaluation for symptoms suggestive of hypertensive crisis or hypertensive encephalopathy. Spravato is contraindicated in patients for whom blood-pressure or intracranial-pressure increases pose serious risk, including aneurysmal vascular disease or arteriovenous malformation, and in those with a history of intracerebral haemorrhage. EU product information similarly specifies baseline blood-pressure assessment and post-dose reassessment at around 40 minutes, and it directs that prescribing be determined by a psychiatrist with treatment delivered in an appropriate clinical setting. citeturn31view3turn31view4turn20view0

Sedation, dissociation and cognitive effects are operationally managed as predictable, time-limited phenomena. In clinical trials, 48%–61% of esketamine-treated patients developed sedation based on the Modified Observer’s Assessment of Alertness/Sedation scale. The label describes short-term cognitive impairment peaking at around 40 minutes post-dose in healthy volunteers, and it includes dedicated on-road driving studies; as a result, patients are counselled not to drive or operate machinery until the next day after a restful sleep. Respiratory depression is a recognised risk: the FDA label notes that patients may display diminished or less apparent breathing during sedation and that post-marketing cases of respiratory depression have been reported. citeturn31view3turn31view4turn34view2turn34view3

Abuse potential and dependence liability are treated as clinically salient, reflecting both ketamine’s history as a drug of misuse and esketamine’s own subjective effects. In the US, esketamine is handled as a Schedule III controlled substance and the label warns of abuse and misuse. FDA reviews report that, in the human abuse potential study in non-dependent recreational polydrug users (N=34), intranasal esketamine produced significantly greater ratings of drug liking than placebo and a signal comparable to intravenous ketamine, supporting the need for restricted distribution and monitoring. In the UK, additional diversion-control measures have been implemented; for example, MHRA-agreed communications describe a Register and Alert System for esketamine intended to mitigate abuse and diversion risk. citeturn7view0turn23search2turn20view8turn17view0

Clinically significant drug–drug interactions are primarily expected via additive sedation and haemodynamic effects rather than strong pharmacokinetic inhibition or induction. The FDA label advises close monitoring when esketamine is used concomitantly with central nervous system depressants (owing to sedation) and with psychostimulants or monoamine oxidase inhibitors (MAOIs) due to blood-pressure elevation. Conversely, esketamine has been studied and routinely used alongside SSRIs and SNRIs, which remain the default oral antidepressant partners under EU and UK indications. With lithium, the evidence base is thinner: lithium augmentation is a standard TRD step in some care pathways, and it featured as an important comparator backdrop in health-technology appraisal work, but there is no labelled pharmacokinetic interaction and it remains unclear whether lithium meaningfully alters esketamine efficacy or tolerability in routine practice; careful clinical monitoring is therefore prudent when combining treatments in complex TRD regimens. citeturn9view0turn20view0turn12search12

Risk minimisation infrastructure is extensive and materially shapes real-world implementation. In the US, Spravato is available only through the Spravato REMS, which requires enrolment, administration under direct observation, and at least 2 hours of monitoring post-dose before discharge if clinically stable. In Canada, Health Canada’s decision materials describe a Controlled Distribution Program designed to manage sedation, dissociation, hypertension, and abuse/diversion risk through enrolment of prescribers, pharmacies and patients, supervised self-administration, and controlled product delivery to the site of care. EU product information similarly requires supervised administration and post-dose monitoring, and UK materials additionally include diversion mitigation via registry systems. citeturn34view3turn18view0turn20view0turn20view8

TRD remains the clearest clinical use case, supported by multiple Phase III trials, relapse-prevention evidence, and growing multi-year exposure datasets. The practical niche is for adults with established non-response to at least two adequate antidepressant trials, particularly where symptom burden is high and clinicians prioritise rapid symptom reduction and functional stabilisation. In real-world delivery, the unmet need is often less whether it works than how to deliver it: clinic throughput, observation capacity, and patient acceptability of repeated supervised visits are major determinants of impact. Both FDA and EU labelling emphasise periodic reassessment of benefit and individualisation of maintenance frequency to the lowest frequency that maintains response. citeturn20view5turn20view6turn20view0turn22search2turn23search18

The evidence base for acute suicidal presentations is best understood as demonstrating rapid reduction in depressive symptoms in the context of comprehensive standard of care rather than a proven anti-suicidal effect. In the two pivotal Phase III studies in adults with MDD and acute suicidal ideation with intent, esketamine improved MADRS scores at 24 hours but did not improve a clinician-rated suicidality severity score (CGI-SS-r) relative to placebo. This creates a clinically important boundary: esketamine may help reduce depressive symptom intensity quickly, but it remains unclear whether it reduces suicidal behaviour, and it should be conceptualised as an adjunct within a broader crisis-care pathway rather than a stand-alone suicide-prevention intervention. citeturn34view1turn34view2turn20view7turn35search13

The US monotherapy indication for TRD is likely to influence near-term practice patterns. For some patients, the earlier requirement to initiate or continue an oral antidepressant was a barrier (prior intolerability, preference, or non-adherence). The monotherapy dataset demonstrates a short-term antidepressant signal over 4 weeks, but the strongest durability evidence and relapse-prevention data remain anchored in combination-therapy programmes. A key next step is therefore rigorous evaluation of whether monotherapy can sustain response over months, what maintenance frequency is required, and whether monotherapy meaningfully changes tolerability or discontinuation rates compared with combination strategies. citeturn20view7turn5view3turn20view6turn35news20

Several emerging applications are attracting research attention but remain earlier-stage than TRD. The literature includes adolescent studies in severe depression with acute suicidal risk (with efficacy signals on depressive symptoms) and investigator-initiated trials in therapy-resistant bipolar depression. These areas face added clinical and regulatory hurdles, including heightened uncertainty around dissociation and abuse-liability in younger populations and the need for robust mood-switch monitoring in bipolar disorder, as well as the challenge of demonstrating durable benefit beyond short-term symptom change. citeturn22search9turn22search26turn20view0

Methodologically, next-generation studies are likely to emphasise comparative and pathway-optimisation designs: head-to-head comparisons against other high-intensity interventions (for example, rTMS, ECT, and structured ketamine infusion programmes), refinement of dosing frequency using longitudinal symptom dynamics, and implementation science that clarifies how to integrate supervised dosing into mental-health systems at scale. Comparative effectiveness evidence is emerging (including analyses comparing intranasal esketamine with rTMS), but it remains too early to claim a stable hierarchy across modalities because patient selection, service intensity, and outcome definitions differ markedly across trials and health systems. citeturn22search21turn22search24