Definition
Esketamine is the S-enantiomer of ketamine — one of the two mirror-image molecular forms (enantiomers) of the ketamine molecule. Marketed under the brand name Spravato by Janssen Pharmaceuticals, esketamine is formulated as a nasal spray and is the first and currently only FDA-approved ketamine-derived medication for psychiatric indications. It received approval in March 2019 for treatment-resistant depression (TRD) and in August 2020 for major depressive disorder (MDD) with acute suicidal ideation or behavior.
The "S" in esketamine refers to the stereochemical configuration of the molecule. In chemistry, enantiomers are non-superimposable mirror images of each other, much like left and right hands. While they share the same chemical formula, their three-dimensional arrangement differs, which can produce distinct pharmacological properties.
Pharmacology
NMDA Receptor Affinity
Esketamine binds to the NMDA receptor with approximately three to four times greater affinity than arketamine (the R-enantiomer). This higher binding affinity makes esketamine a more potent NMDA receptor antagonist per milligram, which is why therapeutic doses of esketamine are typically lower than equivalent doses of racemic ketamine.
Additional Receptor Interactions
Beyond NMDA receptor antagonism, esketamine interacts with several other receptor systems:
- Opioid receptors — Esketamine has measurable affinity for mu and kappa opioid receptors, contributing to its analgesic properties and potentially to its mood effects
- Dopamine transporters — Greater affinity for the dopamine transporter compared to arketamine, which may contribute to psychoactive effects
- Sigma receptors — Interaction with sigma-1 and sigma-2 receptors, the clinical significance of which is still under investigation
- Monoamine transporters — Weak inhibition of serotonin and norepinephrine reuptake at higher concentrations
Metabolism
Esketamine is metabolized primarily by hepatic cytochrome P450 enzymes (CYP2B6 and CYP3A4) to S-norketamine, which retains some pharmacological activity. The half-life of esketamine is approximately 7 to 12 hours when administered intranasally, though the acute psychoactive effects resolve within 1 to 2 hours.
FDA Approval and REMS Program
Approved Indications
- Treatment-resistant depression (TRD) — In conjunction with an oral antidepressant, for adults who have not responded to at least two adequate antidepressant trials — a condition known as treatment-resistant depression
- MDD with acute suicidal ideation or behavior — In conjunction with an oral antidepressant, for short-term treatment of depressive symptoms in adults with MDD who have current suicidal ideation with intent
The REMS Program
Due to concerns about sedation, dissociation, and abuse potential, Spravato is available only through a restricted distribution system called the Risk Evaluation and Mitigation Strategy (REMS). Key requirements include:
- Administration must occur in a certified healthcare setting
- Patients self-administer the nasal spray under healthcare provider observation
- A two-hour post-dose monitoring period is mandatory
- Patients must not drive or operate machinery until the following day
- Healthcare settings and pharmacies must be certified in the REMS program
Dosing Protocol
The standard Spravato dosing schedule is:
- Weeks 1-4 (induction): 56 mg or 84 mg, twice weekly
- Weeks 5-8: 56 mg or 84 mg, once weekly
- Week 9 onward (maintenance): 56 mg or 84 mg, once weekly or every two weeks
Doses are adjusted based on individual tolerability and response. The medication is always used in combination with an oral antidepressant.
How Esketamine Differs From Racemic Ketamine
The key distinctions include:
- Composition — Esketamine is the isolated S-enantiomer; racemic ketamine is a 50:50 mixture of S- and R-enantiomers
- Potency — Esketamine is more potent at the NMDA receptor, requiring lower doses
- Route — Spravato is administered intranasally; racemic ketamine is most commonly given IV or IM
- Regulatory status — Esketamine has specific FDA approval for psychiatric indications; racemic ketamine is used off-label
- Cost and access — Spravato may be covered by insurance but has a high list price; racemic ketamine is typically out of pocket but may be less expensive overall
- Dissociative profile — Esketamine tends to produce a somewhat different subjective experience than racemic ketamine, which some patients and clinicians describe as more "sharp" or "stimulating" compared to the broader, more "enveloping" dissociation of the racemic form
Clinical Significance
Esketamine's FDA approval represented a landmark moment in psychiatry — the first fundamentally new mechanism of action for depression treatment in decades. Its approval validated the glutamate hypothesis of depression and opened the door for further research into ketamine-based and glutamate-targeting therapies.
However, the approval has also generated debate. Critics have noted that the effect sizes in Spravato's registration trials were modest compared to those observed in racemic IV ketamine studies, and that the high cost and REMS requirements limit access. Supporters counter that FDA approval brings regulatory oversight, insurance coverage, and a standardized safety framework that off-label racemic ketamine lacks.
Key Takeaways
- Esketamine is the S-enantiomer of ketamine, marketed as Spravato nasal spray
- It is FDA-approved for treatment-resistant depression and MDD with suicidal ideation
- It has higher NMDA receptor affinity than arketamine, making it more potent per milligram
- Administration is restricted to certified healthcare settings under the REMS program
- Its approval marked a paradigm shift in psychiatric pharmacology toward glutamate-based treatments. For a detailed comparison with racemic ketamine, see our racemic vs esketamine guide. For more on the intranasal Spravato protocols, see our partner resources
References
- MedlinePlus: Esketamine Nasal Spray — National Library of Medicine drug information on esketamine (Spravato), including dosing, side effects, and REMS requirements
- StatPearls: Ketamine — Clinical reference covering ketamine enantiomer pharmacology, including esketamine's receptor binding profile
- Ketamine Pharmacology: An Update — NIH review of ketamine stereoisomer pharmacology and clinical applications
- FDA: Drug Information — FDA resource on approved drug products, including Spravato regulatory history
Share