A Clinical Study of an Investigational Drug for the Treatment of Major Depressive Episode Associated With Bipolar I Disorder.

Inclusion Criteria: Inclusion Criteria (not all inclusive): * Subject provides written informed consent and is willing and able to comply with the protocol in the opinion of the Investigator. * Subject is 18 to 65 years of age, inclusive, at the time of informed consent. * Subject meets DSM-5 criteria, based on the SCID-5-CT, for bipolar I disorder, current episode depressed with or without rapid cycling disease course (≥ 4 episodes of mood disturbance but \< 8 episodes in the previous 12 months) with or without psychotic features. * Subject's current major depressive episode is ≥ 4 weeks and less than 12 months in duration at Screening. * Subject has a MADRS total score ≥ 22 at both Screening and Baseline. * Subject has a CGI-BP-S depression score ≥ 4 at both Screening and Baseline. * Subject has a YMRS total score ≤ 12 at both Screening and Baseline. * Subject is in good physical health, based on medical history, physical examination, neurological examination, vital signs, ECGs, and results of clinical laboratory tests (hematology, chemistry, and urinalysis). Exclusion Criteria: Exclusion Criteria (not all inclusive): * Subject currently has any DSM-5 defined psychiatric diagnosis other than bipolar I disorder that was the primary focus of treatment, or is currently being treated with concomitant medication * Subject has a lifetime history of, or symptoms consistent with, schizophrenia, schizoaffective disorder, or a major psychiatric diagnosis other than bipolar I disorder that is judged to pose risk to the study scientific objectives * Subject has a history of non-response to an adequate (6-week) trial of 3 or more antidepressants (with or without mood stabilizers) during the current major depressive episode. * Subject has any clinically significant unstable medical condition or any clinically significant chronic disease that would pose a risk to the subject or that might confound the results of the study.