Antidepressant Drugs

Correct Answer

B — Esketamine

Rationale

Esketamine (Spravato) is classified as the Food and Drug Administration-approved intranasal formulation for treatment-resistant depression, receiving initial approval in March 2019. A second approval followed in 2020 for major depressive disorder with acute suicidal ideation or behavior. These represent the first non-monoaminergic antidepressant mechanism ever approved by the Food and Drug Administration. Racemic intravenous ketamine is used off-label for treatment-resistant depression but has no Food and Drug Administration approval for psychiatric indications. Vortioxetine is a Food and Drug Administration-approved multimodal serotonergic antidepressant. Agomelatine is not Food and Drug Administration-approved and is available only in Europe and Australia.

Correct Answer

D — Schedule III — moderate abuse potential, accepted medical use

Rationale

Ketamine is classified as a Schedule III controlled substance under the United States Controlled Substances Act, reflecting its established potential for misuse at doses and frequencies higher than those used in medical treatment, while acknowledging its accepted medical uses including anesthetic induction and maintenance. Esketamine shares this Schedule III classification. The Risk Evaluation and Mitigation Strategy program for esketamine directly addresses abuse risk by requiring supervised in-clinic administration and prohibiting take-home dispensing. Schedule I classification applies to substances with no accepted medical use such as heroin. Schedule II applies to substances with high abuse potential and accepted use under severe restriction such as opioids and stimulants. Schedule Four includes substances with lower abuse potential such as benzodiazepines.

Correct Answer

A — Esketamine is the S-enantiomer of ketamine and has approximately three to four times greater affinity for the N-methyl-D-aspartate receptor than the R-enantiomer

Rationale

Ketamine exists as two mirror-image forms (enantiomers). Racemic ketamine — used for intravenous infusion — contains equal proportions of both enantiomers. Esketamine is the S-enantiomer alone and has approximately three to four times greater affinity for the N-methyl-D-aspartate receptor than the R-enantiomer, making it the more pharmacologically potent form. This higher receptor affinity also accounts for esketamine producing more pronounced dissociative effects per unit dose compared to the racemic mixture. Esketamine is not the R-enantiomer and does not have lower receptor affinity. It is not a synthetic analog with a modified chemical structure, nor is it a prodrug — it is the pharmacologically active enantiomer administered directly.

Correct Answer

C — Used off-label for treatment-resistant depression; its licensed indications are anesthetic induction and maintenance, not psychiatric disorders

Rationale

Intravenous racemic ketamine is used off-label for treatment-resistant depression and acute suicidal ideation, supported by a substantial evidence base from multiple randomized controlled trials, but it has no Food and Drug Administration approval for psychiatric indications. Its licensed medical uses are anesthetic induction and maintenance. Because it is off-label, intravenous ketamine for depression is rarely covered by insurance in the United States, making cost a significant barrier. It does not fall under the esketamine Risk Evaluation and Mitigation Strategy program — that program applies specifically to the intranasal esketamine formulation (Spravato). Intravenous ketamine is not classified as investigational; it is an approved drug being used outside its labeled indication, which is the definition of off-label use.

Correct Answer

B — All administration must occur in a certified healthcare setting with at least two hours of post-dose monitoring before the patient is cleared to leave

Rationale

The Risk Evaluation and Mitigation Strategy program for esketamine requires that all administration occur in a certified healthcare setting — patients cannot self-administer or take doses home. After each dose, patients must be monitored for at least two hours before they are cleared to leave. Patients cannot drive on the day of administration. Esketamine must be used in conjunction with an oral antidepressant — it is not approved as monotherapy. These requirements are nationwide regulatory mandates of the Food and Drug Administration approval and are not at the clinician's discretion. Inpatient admission for the first three doses and a 24-hour home caregiver requirement are not part of the Risk Evaluation and Mitigation Strategy program. A psychiatric evaluation before each dose is not a classified Risk Evaluation and Mitigation Strategy requirement.

Correct Answer

A — N-methyl-D-aspartate receptor antagonists

Rationale

Ketamine and esketamine are classified as N-methyl-D-aspartate receptor antagonists — a class that acts on the glutamate system rather than on monoamine reuptake transporters or enzymes. This classification distinguishes them mechanistically from every antidepressant approved before 2019, all of which act on the serotonin, norepinephrine, or dopamine systems. The N-methyl-D-aspartate receptor antagonist class label is the pharmacological basis for ketamine's rapid antidepressant onset (hours rather than weeks) and its distinct clinical profile. Serotonin reuptake transporter inhibitors include the selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors. Melatonin receptor agonists describe agomelatine. Monoamine oxidase inhibitors include phenelzine and tranylcypromine.

Correct Answer

C — Ketamine enters and binds within the channel pore only when the channel is open; channel opening by glutamate is required before ketamine can access its binding site

Rationale

The N-methyl-D-aspartate receptor is a ligand-gated ion channel that requires both glutamate binding and membrane depolarization to open. Ketamine is an open-channel blocker — it gains access to its binding site within the channel pore only after the channel has been opened. Once inside, ketamine physically blocks ion flow, preventing calcium from entering the neuron. This mechanism is called use-dependent because the degree of blockade depends on how frequently the channel opens: channels that are opening more frequently are blocked more effectively. At antidepressant doses, ketamine preferentially blocks N-methyl-D-aspartate receptors in circuits with high activity — including inhibitory interneurons in the prefrontal cortex — without blocking all N-methyl-D-aspartate receptors globally. Ketamine does not bind to the extracellular domain regardless of channel state, does not selectively target depressed brain regions, and does not compete with glutamate at the glutamate binding site.

Correct Answer

A — N-methyl-D-aspartate blockade on inhibitory interneurons releases pyramidal neurons, producing a glutamate burst that activates alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, triggers brain-derived neurotrophic factor release, and drives synaptogenesis within hours

Rationale

The speed of ketamine's antidepressant action is explained by downstream consequences of N-methyl-D-aspartate blockade rather than by the blockade itself. When ketamine blocks N-methyl-D-aspartate receptors on inhibitory interneurons in the prefrontal cortex, those interneurons are silenced, releasing pyramidal neurons from inhibitory control and triggering a rapid burst of glutamate release. This glutamate burst activates alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors on pyramidal neurons, triggering brain-derived neurotrophic factor release and activation of downstream plasticity pathways including the tropomyosin receptor kinase B receptor. This cascade drives rapid synaptogenesis — formation of new synaptic connections in prefrontal circuits — within hours, reversing the synaptic loss caused by chronic stress and depression. Ketamine does not produce its effects through dopamine reuptake inhibition, serotonin autoreceptor desensitization, or global inhibition of excitatory transmission.

Correct Answer

D — The synaptogenesis triggered by ketamine's downstream cascade represents a structural change in prefrontal circuits that persists for days after the drug itself is eliminated

Rationale

Ketamine's antidepressant effect outlasts the drug by days because the mechanism of action is not the blockade itself but the downstream structural changes the blockade initiates. The N-methyl-D-aspartate blockade cascade — glutamate burst, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor activation, brain-derived neurotrophic factor release, synaptogenesis — drives the formation of new synaptic connections in prefrontal circuits within hours. These new synapses represent a structural change in neural architecture that persists for three to seven days after ketamine is eliminated from the body. The drug triggers the structural change; the structural change is what produces the sustained antidepressant benefit. This is entirely different from the mechanism of monoaminergic antidepressants, where drug presence is required to maintain therapeutic monoamine levels. Ketamine's active metabolites, fat tissue accumulation, and serotonin autoreceptor mechanisms do not account for this duration of effect.

Correct Answer

B — Esketamine's dissociative effects — perceptual distortions and feelings of unreality — can precipitate or worsen psychosis in patients with primary psychotic disorders

Rationale

Esketamine produces dose-dependent dissociative effects as a pharmacological consequence of N-methyl-D-aspartate receptor antagonism — perceptual distortions, feelings of unreality, depersonalization, and altered time sense. In patients without psychotic disorders these effects are transient, expected, and resolve within 60 to 90 minutes. In patients with active schizophrenia or other primary psychotic disorders, these dissociative states can trigger or worsen psychotic episodes — a risk that makes active psychosis a clinical contraindication for both esketamine and intravenous ketamine. Esketamine does not inhibit cytochrome P450 2D6, does not produce dangerous blood pressure interactions with antipsychotics through cardiovascular mechanisms, and does not reverse clozapine's mechanism of action through N-methyl-D-aspartate receptor pathways.

Correct Answer

C — Esketamine is approved only as an adjunctive treatment to an oral antidepressant; its clinical trials were conducted in combination with oral antidepressants and it is not approved as monotherapy

Rationale

Esketamine's Food and Drug Administration approval requires that it be used in conjunction with an oral antidepressant — monotherapy is not an approved use. The pivotal clinical trials that established esketamine's efficacy and safety were conducted in patients who were also receiving an oral antidepressant, making combination the evidentiary basis for approval. This is a regulatory requirement of the approval, not a pharmacological necessity — the oral antidepressant does not enhance esketamine's mechanism or prevent adverse effects through a defined pharmacological interaction. Schedule III status does not require co-administration with a non-scheduled agent. The rationale involving serotonin autoreceptor desensitization describes a monoaminergic mechanism that does not apply to esketamine's glutamatergic pharmacology.

Correct Answer

A — Ketamine has sympathomimetic activity through inhibition of catecholamine reuptake, raising sympathetic tone and producing dose-dependent increases in heart rate and blood pressure

Rationale

Ketamine inhibits the reuptake of catecholamines — particularly norepinephrine — at sympathetic nerve terminals, increasing norepinephrine availability in the synapse and raising sympathetic cardiovascular tone. At antidepressant doses, this produces blood pressure increases of approximately 10 to 20 mmHg systolic, peaking during the infusion or shortly after nasal dosing and returning to baseline within one to two hours. Patients with baseline hypertension, significant cardiac disease, or a history of hypertensive emergency require blood pressure optimization before treatment and closer monitoring during the session. Vital signs are measured before administration, at regular intervals during the monitoring period, and before discharge. Ketamine does not produce cardiovascular effects through direct alpha-1 receptor stimulation, histamine H1 blockade, or a baroreceptor-mediated mechanism in the nucleus tractus solitarius.

Correct Answer

D — Esketamine's sympathomimetic activity produces transient blood pressure elevation that could rupture an aneurysm or arteriovenous malformation

Rationale

Ketamine and esketamine produce transient increases in blood pressure through sympathomimetic activity — inhibition of catecholamine reuptake raises norepinephrine levels at sympathetic synapses and increases cardiovascular tone. In a patient with an intracranial aneurysm or arteriovenous malformation, this sudden blood pressure elevation may be sufficient to rupture the structurally compromised vessel wall, causing potentially fatal intracranial hemorrhage. The same mechanism places intracerebral hemorrhage as another absolute contraindication — the blood pressure elevation is contraindicated in any setting where a fragile vascular structure could rupture. Esketamine does not reduce blood pressure (ruling out the perfusion-reduction rationale), does not impair cerebral autoregulation through N-methyl-D-aspartate blockade in a way that produces dangerous flow fluctuations, and does not raise intracranial pressure through metabolic rate changes as the primary mechanism of concern.

Correct Answer

B — Ketamine-induced uropathy is associated with chronic high-dose recreational use — doses and frequencies far exceeding those used in antidepressant treatment — and is not a recognized risk of controlled therapeutic dosing

Rationale

Ketamine-induced uropathy — characterized by severe bladder inflammation, reduced bladder capacity, and potentially permanent structural damage — has been documented in individuals who use ketamine chronically at recreational doses that are substantially higher than the controlled antidepressant dosing of 0.5 mg per kilogram given infrequently. The mechanism is not fully established but is thought to relate to direct toxic effects on urothelial cells from high cumulative ketamine exposure. At the doses and frequencies used in antidepressant treatment — typically six infusions over two weeks or twice-weekly to monthly esketamine dosing — this risk is not established. This distinction between recreational and therapeutic use patterns is clinically relevant for counseling patients and addressing their concerns about long-term safety. Ketamine-induced uropathy is not a recognized complication of standard antidepressant infusion protocols, is not caused by infusion solution acidity, and is not a direct N-methyl-D-aspartate receptor effect on bladder smooth muscle at therapeutic doses.

Correct Answer

D — N-methyl-D-aspartate blockade on inhibitory interneurons triggers a glutamate burst that activates alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, releases brain-derived neurotrophic factor, and drives synaptogenesis in prefrontal circuits within hours

Rationale

Ketamine's rapid antidepressant effect results from downstream consequences of N-methyl-D-aspartate receptor blockade. When ketamine blocks N-methyl-D-aspartate receptors on inhibitory interneurons in the prefrontal cortex, those interneurons are silenced, releasing pyramidal neurons from inhibitory control and producing a burst of glutamate release. This glutamate burst activates alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors on pyramidal neurons, triggering brain-derived neurotrophic factor release and rapid synaptogenesis — formation of new synaptic connections in prefrontal circuits within hours. This structural change reverses the synaptic loss caused by chronic stress and depression and is the pharmacological basis for the response this patient is experiencing. Ketamine does not act through the serotonin reuptake transporter or autoreceptor desensitization, does not produce antidepressant effects through dissociative euphoria, and does not primarily act through dopamine reward circuits at antidepressant doses.

Correct Answer

B — Esketamine's dissociative effects can precipitate or worsen psychosis in patients with active primary psychotic disorders

Rationale

Esketamine produces dose-dependent dissociative effects — perceptual distortions, feelings of unreality, depersonalization, and altered time sense — as a pharmacological consequence of N-methyl-D-aspartate receptor antagonism. In patients without psychotic disorders, these effects are transient and expected. In patients with active schizophrenia or other primary psychotic disorders, these dissociative states can trigger or worsen psychotic episodes. This risk makes active psychosis a clinical contraindication for esketamine and intravenous ketamine. The contraindication is pharmacodynamic — based on the drug's receptor effects and their interaction with the patient's psychopathology — not pharmacokinetic. Esketamine does not inhibit cytochrome P450 3A4, does not produce dangerous cardiovascular interactions with antipsychotics through the mechanism described, and does not block clozapine's mechanism of action through N-methyl-D-aspartate receptor pathways.

Correct Answer

A — Dissociation is a dose-dependent pharmacological effect of N-methyl-D-aspartate receptor antagonism at antidepressant doses and is expected to resolve within 60 to 90 minutes

Rationale

Dissociation — perceptual distortions, feelings of unreality, depersonalization, and altered time sense — is the most consistent acute effect of esketamine at antidepressant doses. It is a pharmacological consequence of N-methyl-D-aspartate receptor antagonism and is expected, not a sign of adverse reaction or dose error. These effects begin within 10 to 20 minutes of intranasal dosing, peak around 30 to 40 minutes, and resolve within 60 to 90 minutes in most patients. The two-hour mandatory monitoring period under the Risk Evaluation and Mitigation Strategy program is designed in part to ensure that dissociation has resolved before the patient is cleared to leave. Patients should be informed before the first treatment that perceptual changes will occur and will resolve. The symptoms described are not consistent with serotonin syndrome, are not evidence of an excessive dose, and are not caused by the oral antidepressant.

Correct Answer

C — Ketamine triggers synaptogenesis within hours; the new synaptic connections persist for several days after the drug is eliminated, but eventually undergo natural turnover without ongoing ketamine to re-trigger their formation

Rationale

Ketamine is eliminated from plasma within a few hours of the infusion, but the downstream structural changes it triggers — rapid synaptogenesis in prefrontal circuits — persist for three to seven days. These new synaptic connections represent the structural basis for the antidepressant effect. As synapses undergo their normal biological turnover cycle and are not re-triggered by additional ketamine, the structural benefit fades and depressive symptoms return. This time course explains the clinical observation of multi-day antidepressant benefit from a single dose and the rationale for repeated infusion courses to extend benefit. Ketamine does not accumulate in brain lipid membranes with a five-to-seven-day half-life, does not produce five-to-seven-day N-methyl-D-aspartate receptor desensitization as its antidepressant mechanism, and does not increase serotonin synthesis — its mechanism is glutamatergic, not serotonergic.