A Study to Evaluate the Efficacy, Pharmacokinetics, Safety and Tolerability of Flexible Doses of Intranasal Esketamine Plus an Oral Antidepressant in Adult Participants With Treatment-resistant Depression

Change From Baseline in Depressive Symptoms as Measured by the MADRS Total Score to 24 Hours Post First Dose (Day 2)

The MADRS is a clinician-rated scale designed to measure depression severity and detects changes due to antidepressant treatment. The scale consists of 10 items (apparent sadness, reported sadness, inner tension, sleep, appetite, concentration, lassitude, inability to feel (interest level), pessimistic thoughts, and suicidal thoughts), each of which is scored from 0 (item not present or normal) to 6 (severe or continuous presence of the symptoms), summed for a total possible score range of 0 to 60. Higher scores represent a more severe condition. Negative change in score indicates improvement.

Time frame: Baseline (Day 1: predose) to 24 hours post first dose (Day 2)

Change From Baseline in Sheehan Disability Scale (SDS) Total Score to the End of Double-blind Treatment Phase (Day 28)

The SDS is a subject-reported outcome measure that consists of a 5-item questionnaire which has been widely used and accepted for assessment of functional impairment and associated disability. The first three items assess disruption of (1) work/school, (2) social life, and (3) family life/home responsibilities using a 0-10 rating scale. The score for the first three items are summed to create a total score of 0-30, where a higher score indicates greater impairment. It also has one item on days lost from school or work and one item on days when underproductive.

Time frame: Baseline up to end of the double-blind treatment phase (Day 28)

Percentage of Participants With Onset of Clinical Response

Onset of clinical response is defined as greater than or equal to (\>=) 50 percent (%) improvement from baseline in MADRS total score with onset by Day 2 that was maintained through Day 28. The MADRS scale consists of 10 items (apparent sadness, reported sadness, inner tension, sleep, appetite, concentration, lassitude, inability to feel (interest level), pessimistic thoughts, and suicidal thoughts), each of which is scored from 0 (item not present or normal) to 6 (severe or continuous presence of the symptoms), summed for a total possible score range of 0 to 60. Higher scores represent a more severe condition. Negative change in score indicates improvement.

Time frame: Day 2 up to Day 28

Percentage of Responders at the End of Double-blind Treatment Phase (Day 28)

Percentage of responders at the end of double-blind treatment phase (Day 28) were assessed. A participant was defined as a responder at a given time point if the percent improvement from baseline in MADRS total score is at least 50%. The MADRS scale consists of 10 items (apparent sadness, reported sadness, inner tension, sleep, appetite, concentration, lassitude, inability to feel (interest level), pessimistic thoughts, and suicidal thoughts), each of which is scored from 0 (item not present or normal) to 6 (severe or continuous presence of the symptoms), summed for a total possible score range of 0 to 60. Higher scores represent a more severe condition. Negative change in score indicates improvement.

Time frame: Day 28

Percentage of Participants in Remission at the End of Double-blind Treatment Phase (Day 28)

Percentage of participants in remission at the end of double-blind treatment phase (Day 28) were assessed. A participant was considered as a remitter if participant had a MADRS total score of less than or equal to \[\<=\] 12 at a visit. MADRS scale consists of 10 items (apparent sadness, reported sadness, inner tension, sleep, appetite, concentration, lassitude, inability to feel (interest level), pessimistic thoughts, and suicidal thoughts), each of which is scored from 0 (item not present or normal) to 6 (severe or continuous presence of the symptoms), summed for a total possible score range of 0 to 60. Higher scores represent a more severe condition. Negative change in score indicates improvement.

Time frame: Day 28

Percentage of Participants With Sustained Remission

Sustained remission is defined as the first occurrence of remission (MADRS Total score \<=12) that was maintained through the Day 28 assessment with one excursion prior to Day 28. The MADRS scale consists of 10 items (apparent sadness, reported sadness, inner tension, sleep, appetite, concentration, lassitude, inability to feel (interest level), pessimistic thoughts, and suicidal thoughts), each of which is scored from 0 (item not present or normal) to 6 (severe or continuous presence of the symptoms), summed for a total possible score range of 0 to 60. Higher scores represent a more severe condition. Negative change in score indicates improvement.

Time frame: Up to Day 28

Change From Baseline in Clinical Global Impression Severity (CGI-S) Scale Score up to the Endpoint (Double-blind Treatment Phase [Day 28])

The CGI-S provides an overall clinician-determined summary measure of the severity of the participant's illness that takes into account all available information, including knowledge of the participant's history, psychosocial circumstances, symptoms, behavior, and the impact of the symptoms on the participant's ability to function. The CGI-S evaluates the severity of psychopathology on a scale of 1 to 7. Considering total clinical experience, a participant is assessed on severity of mental illness at the time of rating according to: 1=normal (not at all ill); 2=borderline mentally ill; 3=mildly ill; 4=moderately ill; 5=markedly ill; 6=severely ill; 7=among the most extremely ill patients. The CGI-S permits a global evaluation of the participant's condition at a given time. Negative change in score indicates improvement. The last post-baseline observation during the double-blind phase was carried forward as Endpoint.

Time frame: Baseline up to Double-blind Endpoint (Day 28)

Change From Baseline in Generalized Anxiety Disorder 7-item (GAD-7) Scale Score up to the Endpoint (Double-blind Treatment Phase [Day 28])

The GAD-7 is a brief and validated 7-item self-reported assessment of overall anxiety. Participants respond to each item using a 4 point scale with response categories of 0=not at all, 1=several days, 2=more than half the days, and 3=nearly every day. Item responses are summed to yield a total score with a range of 0 to 21, where higher scores indicate more anxiety. The recall period is 2 weeks. The severity of the GAD-7 is categorized as follows: None (0-4), Mild (5-9), Moderate (10-14) and Severe (15-21). The last post-baseline observation during the double-blind phase was carried forward as the "Endpoint".

Time frame: Baseline up to Endpoint (double-blind treatment phase [Day 28])

Change From Baseline in Participant-Reported Health-Related Quality of Life as Assessed by EuroQol-5 Dimension-5 Level (EQ-5D-5L) Score up to the Endpoint (Double-blind Treatment Phase [Day 28]): Health Status Index

The EQ-5D-5L is a standardized 2-part instrument for use as a measure of health outcome, primarily designed for self-completion by respondents. It essentially consists of the EQ-5D-5L descriptive system and the EQ Visual Analogue Scale (EQ-VAS). The EQ-5D-5L descriptive system comprises the following 5 dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each of the 5 dimensions is divided into 5 levels of perceived problems (Level 1 indicating no problem, Level 2 indicating slight problems, Level 3 indicating moderate problems, Level 4 indicating severe problems, and Level 5 indicating extreme problems). Participant selects answer for each of 5 dimensions considering response that best matches his/her health "today". Responses were used to generate a HSI. Health Status Index ranges from -0.148 to 0.949, and is anchored at 0 (dead) and 1 (full health), a lower score indicates worse health.

Time frame: Baseline up to Double-blind Endpoint (Day 28)

Change From Baseline in Participant-Reported Health Status as Assessed by EuroQol-5 Dimension-5 Level (EQ-5D-5L) Score up to the Endpoint (Double-blind Treatment Phase [Day 28]): Visual Analogue Scale (VAS)

The EQ-5D-5L is a standardized 2-part instrument for use as a measure of health outcome, primarily designed for self-completion by respondents. It essentially consists of the EQ-5D-5L descriptive system and the EQ-VAS. EQ-VAS self-rating records the respondent's own assessment of his/her overall health status at time of completion, on a scale of 0 (worst health you can imagine) to 100 (best health you can imagine). Positive change in score indicates improvement.

Time frame: Baseline up to Double-blind Endpoint (Day 28)

Change From Baseline in Participant-Reported Health Status as Assessed by EuroQol-5 Dimension-5 Level (EQ-5D-5L) up to the Endpoint (Double-blind Treatment Phase [Day 28]): Sum Score

EQ-5D-5L consists of EQ-5D-5L descriptive system and EQ visual analogue scale (EQ-VAS). EQ-5D-5L descriptive system comprises of 5 dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each has 5 levels of perceived problems (1-no problem, 2-slight problems, 3-moderate problems, 4-severe problems, 5-extreme problems). Participant selects answer for each of 5 dimensions considering response that best matches his/her health "today". Responses were used to generate a Health Status Index (HSI). HSI ranges from -0.148 to 0.949 and is anchored at 0 (health state value equal to dead) and 1 (full health). EQ-VAS self-rating records the respondent's own assessment of his/her overall health status at time of completion, on a scale of 0 (worst health you can imagine) to 100 (best health you can imagine). Sum score ranges from 0 to 100 where, sum score = (sum of the scores from the 5 dimensions minus 5) \*5. Higher score indicates worst health state.

Time frame: Baseline up to Double-blind Endpoint (Day 28)