Nitrous Oxide as a Putative Novel Dual-Mechanism Treatment for Bipolar Disorder

This study was terminated due to COVID-19 pandemic-related halting of recruitment in the context of an upcoming replacement of the study MRI scanner.

This study is a 7-day randomized, double-blind proof-of-concept pilot study of nitrous oxide vs. midazolam in 40 adults (20-60 years) with bipolar disorder (BD) (type I or II). Ongoing pharmacological and psychosocial treatments may continue, provided that they have not been initiated or significantly modified in the preceding 2 weeks. Participants' current treatment as prescribed by clinical psychiatrists will not be modified or interfered in this study. The study involves 3 visits. During study visit 1, participants will complete screening to ensure study eligibility. This will be done using interview measures. During study visit 2, participants will complete anthropomorphic measurements, measurement of endothelial function, screening blood work, ECGs, and an anaesthesia screener. During study visit 3, participants will receive the treatment (nitrous oxide or midazolam), complete an MRI scan, and complete interview measures and self-reports. There will be anthropomorphic measurements taken as well. The participant will be required to complete phone interviews and self-reports over the subsequent 7 days. There are 4 main predictions: 1. Nitrous oxide will significantly reduce depression symptoms vs. midazolam. 2. Nitrous oxide will significantly increase frontal cortical perfusion vs. midazolam. 3. Lower perfusion in frontal cortical regions at baseline will be associated with greater improvement in depression symptoms following nitrous oxide treatment. 4. Poorer endothelial function will be associated with greater improvement in depression symptoms following nitrous oxide treatment.

N2O-condition participants will inhale an initial mixture of 10% N2O in oxygen (O2) for 5 minutes, followed by 25% N2O in O2 for 20 minutes. N2O-condition participants will also receive 5ml intravenous saline concomitantly with 10% N2O, and again with 25% N2O.

Inhaled room air plus intravenous midazolam bolus (total 2mg). Midazolam-condition participants will receive intravenous infusions of 0.5mg midazolam in 5ml saline (start of 1st inhalation epoch), followed by 1.5mg midazolam in 5ml saline (start of 2nd inhalation epoch).

Measures mood symptom severity, used to select patients and assess treatment efficacy. Although other time-points will be examined, 24h was selected as the primary outcome to minimize the impact of acute sedation and psychoactive effects.

Assessed at baseline, an average of 3 days later, again at up to 5 days after baseline on the day of drug administration, and participants will be followed for 7 days after the drug administration

Assessed at baseline, an average of 3 days later, again at up to 5 days after baseline on the day of drug administration, and participants will be followed for 7 days after the drug administration

Measured an average of 3 days post-baseline and again approximately every hour on the drug administration day

Measured an average of 3 days post-baseline and again approximately every hour on the drug administration day

B12 and nitric oxide (NO) will be examined as predictors of response owing to known associations with the mechanism of action of N2O.

Inclusion Criteria: English-speaking; age 20-60 years; BD-I or BD-II, current major depressive episode ≥4 weeks duration; MADRS≥22; taking ≥1 mood stabilizing medication/s (i.e. antimanic anticonvulsant, antipsychotic, and/or lithium). Exclusion Criteria: New medications or changes in dosing, or ECT or TMS, in the preceding 2 weeks; MADRS item 10, > 4; YMRS≥12; acute significant suicidality; psychosis; substance abuse (past 3 months); active major medical conditions (hepatic, renal, respiratory, or cardio/cerebrovascular disease; diabetes; esophageal reflux; sleep apnea); B12 deficiency/disorders; pregnant; MRI contraindications; history of adverse anaesthetic reactions; anaesthesia class >2; scuba diving in preceding week.

Dimick MK, Omrin D, MacIntosh BJ, Mitchell RHB, Riegert D, Levitt A, Schaffer A, Belo S, Iazzetta J, Detzler G, Choi M, Choi S, Orser BA, Goldstein BI. Nitrous oxide as a putative novel dual-mechanism treatment for bipolar depression: Proof-of-concept study design and methodology. Contemp Clin Trials Commun. 2020 Jun 23;19:100600. doi: 10.1016/j.conctc.2020.100600. eCollection 2020 Sep.

Kim WSH, Dimick MK, Omrin D, Mitchell RHB, Riegert D, Levitt A, Schaffer A, Belo S, Iazzetta J, Detzler G, Choi M, Choi S, Herrmann N, McIntyre RS, MacIntosh BJ, Orser BA, Goldstein BI. Proof-of-concept randomized controlled trial of single-session nitrous oxide treatment for refractory bipolar depression: Focus on cerebrovascular target engagement. Bipolar Disord. 2023 May;25(3):221-232. doi: 10.1111/bdi.13288. Epub 2023 Jan 5.