Expert opinion on drug metabolism & toxicology
January 1, 2026
Yang Jing Zheng, Christine E Dri, Sabrina Wong et al.
Dextromethorphan/bupropion (DXM/BUP) received breakthrough FDA approval in August 2022 as a rapid-acting antidepressant. DXM/BUP is a noncompetitive NMDA receptor antagonist and sigma-1 receptor agonist, combined with bupropion, a norepinephrine/dopamine reuptake inhibitor and CYP2D6 inhibitor. DXM alone has long been misused due to its metabolism into the psychoactive metabolite dextrorphan (DXO). The article discusses the pharmacodynamics and pharmacokinetics of DXM and DXO, highlights the abuse potential of DXM alone, and presents preclinical, clinical, and pharmacovigilance findings that support reduced abuse liability of DXM/BUP. The formulation demonstrates clinically meaningful improvement within one week of initiation. Given its safety, efficacy, and novelty, this glutamatergic modulator is a promising candidate for global approval. Future research should examine its potential in bipolar depression and trauma-associated MDD.
CNS drugs
October 1, 2023
Dania Akbar, Taeho Greg Rhee, Felicia Ceban et al.
A systematic review of five studies found that AXS-05, a combination of dextromethorphan and bupropion, rapidly reduces depression severity in adults with major depressive disorder who do not respond to standard antidepressants. Depressive symptoms measured on the MADRS scale decreased significantly compared to placebo as early as one week and compared to an active control at two weeks. The treatment effect was maintained for up to 12 months, with an average 23-point reduction from baseline. The therapy was well-tolerated with only transient side effects. These results support the role of glutamatergic and sigma-1 signaling pathways in depression.
Bipolar disorders
May 1, 2023
William S H Kim, Mikaela K Dimick, Danielle Omrin et al.
In a double-blind randomized controlled trial, 25 adults with bipolar I or II disorder and treatment-resistant depression received either nitrous oxide (25% concentration for 20 minutes) plus intravenous saline or medical air plus intravenous midazolam (2 mg total). No significant between-group differences emerged in depression severity change or treatment response 24 hours after treatment. However, the nitrous oxide group showed significantly greater same-day reductions in depression severity. Lower baseline regional cerebral blood flow predicted greater 24-hour improvement with nitrous oxide but not midazolam. Midazolam was associated with regional cerebral blood flow reductions compared to nitrous oxide. These secondary findings suggest differential associations of the two agents with depression severity and brain hemodynamics, warranting larger studies.
Journal of affective disorders
December 1, 2022
Anastasia Levinta, Shakila Meshkat, Roger S McIntyre et al.
Ketamine rapidly reduces depressive symptoms in people with treatment-resistant depression, but its effectiveness may diminish as the number of prior failed treatments increases. A systematic review of 18 randomized controlled trials found that ketamine and esketamine worked at both lower and higher stages of treatment resistance, yet effect sizes and duration of benefits were greater in studies involving patients with fewer prior antidepressant failures. Variability in how studies defined treatment resistance and measured outcomes prevented clear comparisons of efficacy across different resistance stages. The authors conclude that while ketamine remains broadly effective, more failed treatment trials may reduce its efficacy, and participant-level data are needed to clarify the relationship between resistance level and response.
Journal of affective disorders
October 15, 2022
Isak Joneborg, Yena Lee, Joshua D Di Vincenzo et al.
A systematic review of five randomized-controlled trials found that ketamine-assisted psychotherapy (KAP) had a significant positive effect on primary outcome measures for adults with substance use disorders and treatment-resistant depression, but the data is mixed. The single trial examining KAP for treatment-resistant depression found no benefit. The review notes a lack of large, replicated clinical trials and no studies actively examining mechanisms of action. Evidence suggests temporary neural changes caused by ketamine, such as NMDAR inhibition and increased synaptic neuroplasticity, may affect treatment outcomes. Preliminary findings also suggest adjunct psychotherapy, changes in perspective, and spirituality may play a role.