Maintenance Ketamine Infusions for Treatment-Resistant Bipolar Depression

Inclusion Criteria:

1. Provide written, voluntary informed consent prior to study enrollment. Substitutedecision makers will not be allowed to consent to study on a potential patient'sbehalf.
2. Male or female between the age of 21 to 65, inclusive.
3. Meets DSM-5 criteria for Bipolar I or II Disorder, currently experiencing a MajorDepressive Episode without psychotic features. Diagnosis confirmed by studypsychiatrist at the start of the parent KET-BD randomized clinical trial (RCT).
4. Patients in the KET-BD RCT 4a. Patients in the ketamine arm of the KET-BD RCT musthave experienced an antidepressant response (i.e. change in MADRS score ≥ 50% at day 14 compared to baseline or Clinical Global Impression-Improvement (CGI-I) = 2 'muchimproved' or 1 'very much improved') or experienced clinical remission of symptoms (i.e., MADRS score < 12 on day 14) 4b. Patients in the midazolam arm of the KET-BD RCTmust present as moderately to severely depressed (MADRS >21) on days 14 and 28 of theparent RCT and must be responders or remitters following four flexibly dosed infusionsover 2 weeks.
5. Current depressive episode has inadequate response to two or more adequate first-linetreatment trials for bipolar depression, as per the 2018 CANMAT Bipolar DisorderGuidelines. First line treatment trials include the use of lithium, valproate,carbamazepine, lamotrigine and/or any antipsychotic medication. Adequate medicationsconfirmed at the start of the parent KET-BD RCT.
6. Patient must be receiving guideline-concordant pharmacotherapy without changes in thelast month, including a therapeutic dose of a mood stabilizer.

Exclusion Criteria:

1. Currently exhibiting symptoms of mania, hypomania, or mixed state bipolar, asdetermined by the Young Mania Rating Scale (YMRS) score greater than 12.
2. Current symptoms of psychosis or a substance use disorder within the past 3 months.History of psychotic features during a mood episode will not be excluded.
3. History of neurological disorders (including, but not limited to, uncontrolled seizuredisorder, history of stroke within past 12 months, major head injuries, aneurysmalvascular disease [including thoracic and abdominal aorta, intracranial, and peripheralarterial vessels], arteriovenous malformation, or intracerebral hemorrhage)
4. Lifetime history of a primary psychotic disorder (including, but not limited to,schizophrenia or schizoaffective disorder)
5. Lifetime history of ketamine use disorder
6. Presence of active suicidality, requiring involuntary inpatient treatment or recentsuicide attempts within the past 3 months.
7. Presence of a contraindication to ketamine, including a drug allergy, uncontrolledhypertension (baseline systolic blood pressure > 140 mmHg and/or diastolic bloodpressure > 90 mmHg), low or labile blood pressure, myocardial infarction within past 12 months, cardiac arrhythmia, moderate to severe hepatic impairment (i.e., Child-Pughscore of B or C), moderate or severe renal impairment (glomerular filtration rate (GFR) < 45 milliliters/min), heart failure, or coronary artery disease
8. Pregnant or breastfeeding women or women who intend to get pregnant. Patients who aresexually active must agree to use a highly effective contraceptive method (as outlinedin section 5.9).
9. Use of prohibited concomitant medications, including other forms of ketamine oresketamine, benzodiazepines, monoamine oxidase inhibitors, stimulants, medical orrecreational cannabis of any form.
10. Patients in the ketamine-arm of the parent RCT, that did not reasonably tolerate 4infusions of flexibly-dosed ketamine, as determined by the investigator and/or patient