A Study to Assess the Efficacy and Safety of TC-5214 as an Adjunct Therapy in Patients With Major Depressive Disorder

• Response in Depressive Symptoms of Major Depressive Disorder (MDD), Defined as a ≥50% Reduction From Randomization (Week 8) in MADRS Total Score at End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]

  The percentage of patients with a ≥50% reduction from randomization (Week 8) in MADRS total score at end of treatment (Week 16) was calculated.

  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.

• Remission in Depressive Symptoms of MDD, Defined as MADRS Total Score of ≤8 at End of Treatment (Week 16) [ Time Frame: Week 16 ] [ Designated as safety issue: No ]

  The percentage of patients with a MADRS total score of ≤8 at end of treatment (Week 16) was calculated.

  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.

• Early and Sustained Response, Defined as a ≥50% Reduction From Randomization (Week 8) in MADRS Total Score and a MADRS Total Score of ≤12 at Week 10, Week 12, Week 14, and End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16); Week 10, Week 12, Week 14, and Week 16 ] [ Designated as safety issue: No ]

  The percentage of patients with a ≥50% reduction from randomization (Week 8) in MADRS total score and a MADRS total score of ≤12 at Week 10, Week 12, Week 14, and end of treatment (Week 16) was calculated.

  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.

• Sustained Response, Defined as a ≥50% Reduction From Randomization (Week 8) in MADRS Total Score and a MADRS Total Score of ≤12 at Week 12, Week 14, and End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16); Week 12, Week 14, and Week 16 ] [ Designated as safety issue: No ]

  The percentage of patients with a ≥50% reduction from randomization (Week 8) in MADRS total score and a MADRS total score of ≤12 at Week 12, Week 14, and end of treatment (Week 16) was calculated.

  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.

• Sustained Remission, Defined as a MADRS Total Score of ≤8 at Week 12, Week 14, and End of Treatment (Week 16) [ Time Frame: Week 12, Week 14, Week 16 ] [ Designated as safety issue: No ]

  The percentage of patients with a MADRS total score of ≤8 at Week 12, Week 14, and end of treatment (Week 16)was calculated.

  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.

• Change in Depressive Symptoms From Randomization (Week 8) to End of Treatment (Week 16) as Measured by Hamilton Rating Scale for Depression-17 Items (HAMD-17) Total Score [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 17-item, clinician-rated scale that assesses depressive symptoms. The HAMD-17 consists of 17 symptoms, each of which is rated from 0 to 2 or 0 to 4, where 0 is none/absent. The HAMD-17 total score is calculated as the sum of the 17 individual symptom scores; the total score can range from 0 to 52. Higher HAMD-17 scores indicate more severe depression.
• Change in the Clinician-rated Global Outcome of Severity as Measured by the Clinical Global Impression-Severity (CGI-S) Score From Randomization (Week 8) to End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 3-part, clinician-administered scale that rates the improvement or worsening of the patient's illness from randomization (baseline). Each item is scored on a 1 to 7 scale. Higher CGI-S scores indicate greater illness severity.
• Response in the Clinical Global Impression-Improvement (CGI-I) Defined as CGI-I Rating of "Very Much Improved" or "Much Improved" From Randomization (Week 8) to End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 3-part, clinician-administered scale that rates the improvement or worsening of the patient's illness from randomization (baseline). Each item is scored on a 1 to 7 scale. CGI-I scores >4 indicate worsening, while scores <4 indicate improvement.
• Change in Hamilton Anxiety Scale (HAM-A) Total Score From Randomization (Week 8) to End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 14-item clinician-administered scale for the evaluation of anxiety symptoms. Each HAM-A item is rated on a 0 to 4 scale, the total score can range from 0 to 56. Higher HAM-A scores indicate higher levels of anxiety.
• Change in MADRS Total Score From Randomization (Week 8) to Week 9 [ Time Frame: Randomization (Week 8) to Week 9 ] [ Designated as safety issue: No ]
  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.
• Change in MADRS Total Score From Randomization (Week 8) to Week 10 [ Time Frame: Randomization (Week 8) to Week 10 ] [ Designated as safety issue: No ]
  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.
• Change in MADRS Total Score From Randomization (Week 8) to Week 12 [ Time Frame: Randomization (Week 8) to Week 12 ] [ Designated as safety issue: No ]
  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.
• Change in MADRS Total Score From Randomization (Week 8) to Week 14 [ Time Frame: Randomization (Week 8) to Week 14 ] [ Designated as safety issue: No ]
  A 10-item scale for the evaluation of depressive symptoms. Each MADRS item is rated on a 0 to 6 scale. The MADRS total score is calculated as the sum of the 10 individual item scores; the total score can range from 0 to 60. Higher MADRS scores indicate higher levels of depressive symptoms.
• Change in Functional Impairment From Randomization (Week 8) to End of Treatment (Week 16) as Measured by the Sheehan Disability Scale (SDS) Total Score [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  Sheehan Disability Scale (SDS) is 5-item, self-administered scale that measures the extent a patient is impaired by their disease. Higher scores indicate more severe impairment. The SDS total score is calculated as the sum of the score for the 3 inter-correlated domains (school/work, social life, and family life/home responsibilities) and ranges from 0 (unimpaired) to 30 (highly impaired).
• Change in Functional Impairment From Randomization (Week 8) to End of Treatment (Week 16) as Measured by SDS Work/School Domain Score [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 5-item, self-administered scale that measures the extent a patient is impaired by their disease. Higher scores indicate more severe impairment. The 3 inter-correlated domains are school/work, social life, and family life/home responsibilities. The numerical rating for the work/school domain score is 0- 10, where 10 is considered to be 'highly impaired'.
• Change in Functional Impairment From Randomization (Week 8) to End of Treatment (Week 16) as Measured by SDS Social Life Domain Score [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 5-item, self-administered scale that measures the extent a patient is impaired by their disease. Higher scores indicate more severe impairment. The 3 inter-correlated domains are school/work, social life, and family life/home responsibilities. The numerical rating for the SDS social life domain score is 0- 10, where 10 is considered to be 'highly impaired'.
• Change in Functional Impairment From Randomization (Week 8) to End of Treatment (Week 16) as Measured by SDS Family Life/Home Responsibilities Domain Score [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A 5-item, self-administered scale that measures the extent a patient is impaired by their disease. Higher scores indicate more severe impairment. The 3 inter-correlated domains are school/work, social life, and family life/home responsibilities. The numerical rating for the SDS family life/home responsibilities domain score is 0- 10, where 10 is considered to be 'highly impaired'.
• Change in Overall Quality of Life and Satisfaction From Randomization (Week 8) to End of Treatment (Week 16) by Assessing the Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form (Q-LES-Q-SF) % Maximum Total Score [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  The Q-LES-Q-SF total score is derived by summing item scores 1 to 14. Higher scores are indicative of greater enjoyment or satisfaction in each domain. The Q-LES-Q-SF % maximum total score is calculated as 100% × (Q-LES-Q-SF total score - 14) / 56, and can range from 0% to 100%.
• Change From Randomization (Week 8) to End of Treatment (Week 16) in Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form(Q LES-Q-SF)Item 15 [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  The Q-LES-Q-SF (Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form) measures the patient's satisfaction with medication and overall quality of life. The 15th item queries respondents' satisfaction with the medication they are taking, rated on a 1 to 4 scale, score 0 indicates that no medication was taken. Higher scores are indicative of greater satisfaction.
• Change From Randomization (Week 8) to End of Treatment (Week 16) in Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form (Q LES-Q-SF) Item 16 [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  The Q-LES-Q-SF (Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form) measures the patient's satisfaction with medication and overall quality of life. The 16th item is a global rating of overall life satisfaction and contentment, rated on a 1 to 5 scale. Higher scores are indicative of greater satisfaction.
• Change in EuroQol - 5 Dimensions (EQ-5D) From Randomization (Week 8) to End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A self-assessment questionnaire that provides 2 measures of health status. The EQ-5D index score is a weighted linear combination over 5 dimensions of health status. The score for each of the 5 dimensions can range from 1 to 3, and an equation is used to calculate the EQ-5D index score. The EQ-5D index score can range from possible negative values (minimum -0.415) to a maximum of 1.0. The EQ-VAS is a visual analog scale with a range of 0 to 100. For both variables, a higher score indicates a better health state.
• Change in Irritability Symptoms as Measured by the Sheehan Irritability Scale (SIS) Total Score From Randomization (Week 8) to End of Treatment (Week 16) [ Time Frame: Randomization (Week 8) to end of treatment (Week 16) ] [ Designated as safety issue: No ]
  A self-administered scale to be used by clinical subjects to rate suffering over the past week with regard to irritability symptoms. The total SIS score is the sum of 7 items, and ranges from 0 to 70. Each item is assessed on an 11- point scale where 0=not at all, 1-3=mildly, 4-6=moderately, 7-9=markedly, and 10=extremely. The SIS also records the number of days impaired by irritability.

• Changes in clinician-rated symptoms as assessed by MADRS, Hamilton Rating Scale for Depression (HAM-D), Clinical Global Impression Severity (CGI-S), Clinical Global Impression Improvement (CGI-I) and Hamilton Anxiety Scale (HAM-A) [ Time Frame: MADRS and CGI will be scored at Weeks 8 (baseline), 9, 10, 12, 14, and 16; HAM-D and HAM-A will be scored at Weeks 8 (baseline) and 16 ] [ Designated as safety issue: No ]
• Changes in patient-reported outcomes as assessed by Sheehan Disability Scale, Quality of Life Enjoyment and Satisfaction Questionnaire-Short Form, Quick Inventory of Depressive Symptomatology-Self Report-16 (QIDS-SR-16) and Sheehan Irritability Scale [ Time Frame: Will be analysed at Weeks 8, 12 and 16. QIDS-SR-16 will also be measured at Week 10 ] [ Designated as safety issue: No ]
• AEs, SAEs, change in physical exam results and vital signs, laboratory tests and ECG, C-SSRS, BARS and AIMS, CSFQ, and DESS will be assessed as a measure of safety and tolerability [ Time Frame: Will be collected during the whole study period. Unsolicited SAEs will be collected for 30 days post last study treatment ] [ Designated as safety issue: Yes ]

The purpose of this study is to determine if TC-5214 or placebo (a tablet that looks like medicine tablet or capsule, but contains no active medicine) is safe and effective when taken together with another antidepressant.

• Major Depressive Disorder
• Depression

• Drug: TC-5214
  Tablet, oral, twice daily for 8 weeks
• Drug: Placebo
  Tablet, oral, twice daily for 8 weeks

• Experimental: SSRI/Serotonin/SNRI+ TC-5214 0.5 mg
  Selective serotonin reuptake inhibitor (SSRI)/Serotonin/norepinephrine reuptake inhibitor (SNRI) + TC-5214, 0.5 mg BID
  Intervention: Drug: TC-5214
• Experimental: SSRI/Serotonin/SNRI + TC-5214 2 mg
  Selective serotonin reuptake inhibitor (SSRI)/Serotonin/norepinephrine reuptake inhibitor (SNRI) + TC-5214, 2 mg BID
  Intervention: Drug: TC-5214
• Experimental: SSRI/Serotonin/SNRI + TC-5214 4 mg
  Selective serotonin reuptake inhibitor (SSRI)/Serotonin/norepinephrine reuptake inhibitor (SNRI) + TC-5214, 4 mg BID
  Intervention: Drug: TC-5214
• Placebo Comparator: SSRI/Serotonin/SNRI + Placebo
  Selective serotonin reuptake inhibitor (SSRI)/Serotonin/norepinephrine reuptake inhibitor (SNRI) + Placebo BID
  Intervention: Drug: Placebo

Inclusion Criteria:

• Provision of signed and dated informed consent before initiation of any study-related procedures.
• The patient must have a clinical diagnosis of major depressive disorder (MDD) with inadequate response to no more than one antidepressant.
• Outpatient status at enrollment and randomization.

Exclusion Criteria:

• Patients with a lifetime history of bipolar disorder, psychotic disorder or post-traumatic stress disorder.
• Patients with a history of suicide attempts in the past year and/or seen by the investigator as having a significant history of risk of suicide or homicide.
• History of renal insufficiency or impairment or conditions that could affect absorption or metabolism of investigational product.