RESEARCH MONOGRAPH · KDC-MN-171

Esketamine

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

70/100

The patented S-enantiomer, FDA-approved, and an interesting question about whether single-isomer matters

Esketamine is (S)-ketamine, the S-enantiomer of the racemic mixture. Janssen developed it as Spravato (intranasal spray), FDA approved 2019 for treatment-resistant depression and major depressive disorder with acute suicidal ideation. The patent and approval strategy was effectively a way to commercialize one half of an off-patent molecule via novel formulation and chirality.

Mechanism-wise esketamine has higher NMDA receptor affinity than the R-enantiomer (roughly 3-4x at the channel-blocking site), which is the rationale for using the single isomer at lower total doses. The downstream cascade (glutamate surge, AMPA activation, BDNF, mTORC1, synaptic plasticity) is the same general pathway as racemic ketamine. The interesting open question is whether the dissociative experience and the antidepressant effect can be dissociated at the enantiomer level, and esketamine doesnt seem to do that, dissociation tracks with the dosing even with the single isomer.

Clinical efficacy data from Spravato pivotal trials (TRANSFORM, SUSTAIN) showed response in treatment-resistant depression with intranasal delivery alongside an oral antidepressant. Effect sizes are real but modest compared to IV racemic ketamine in many comparative studies, possibly because intranasal bioavailability runs maybe 40-50% and is variable. There's been ongoing debate about whether the trials demonstrated effect-versus-comparator as cleanly as Janssen presented.

Sourcing: as Spravato it's tightly controlled and only administered in REMS-certified clinics. As a research compound, single-isomer S-ketamine is available from research suppliers at higher cost than racemic, with HPLC plus chiral HPLC verification standard.

Safety profile mirrors racemic ketamine for the most part. The intranasal delivery does limit single-dose exposure compared to what's achievable IV.

What we like: the regulatory pathway and the FDA approval established a real precedent for rapid-acting antidepressants, which has downstream benefit for the whole class. What we dont like: the IV racemic versus intranasal esketamine comparison is honestly an open question that the commercial framing has obscured, and a lot of clinicians experienced with both formulations have strong opinions about which produces better response in actual patients.

Worth keeping in the library as the enantiomer-isolated research tool.

Evidence: 80
Mechanism: 82
Reliability: 75
Safety: 68
Sourcing: 65
Value: 35
Signal: 75
Staying power: 78

Plain-language summary Intrigue 82 / 100

Esketamine, sold as Spravato, is the S-enantiomer of ketamine purified out as a single isomer. Approved in 2019 as an intranasal spray for treatment-resistant depression. About twice as potent as racemic ketamine at NMDA receptors. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

S-enantiomer NMDA antagonist

The (S)-enantiomer of ketamine, FDA-approved as Spravato (intranasal) for treatment-resistant depression.

Abstract

Esketamine (Spravato; CAS 33643-46-8) is the (S)-enantiomer of ketamine, FDA-approved in 2019 as an intranasal formulation for treatment-resistant depression and as adjunctive treatment for major depressive disorder with acute suicidal ideation (2020). The (S)-enantiomer carries higher NMDA receptor affinity than the (R)-enantiomer; the racemic ketamine is approximately 60 percent (S)-enantiomer activity. Pharmacokinetics: intranasal bioavailability ~48 percent; plasma half-life 7 to 12 hours. Reported research dose ranges in the literature are described in the source publications. Schedule III. REMS distribution program due to dissociation and abuse risk.

Mechanism of action

S-enantiomer of ketamine; non-competitive NMDA antagonist with higher receptor affinity than R-enantiomer.

Reported research dose ranges

Reported research dose ranges in the literature.

References

Daly EJ, et al. Efficacy and safety of intranasal esketamine adjunctive to oral antidepressant therapy in treatment-resistant depression. JAMA Psychiatry 2018.

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KDC-MN-171

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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Esketamine

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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