Efficacy of Adjunctive D-Cycloserine to Intermittent Theta-Burst Stimulation for Major Depressive Disorder

Importance: The antidepressant effects of transcranial magnetic stimulation protocols for major depressive disorder (MDD) are thought to depend on synaptic plasticity. The theta-burst stimulation (TBS) protocol synaptic plasticity is known to be N-methyl-D-aspartate (NMDA)-receptor dependent, yet it is unknown whether enhancing NMDA-receptor signaling improves treatment outcomes in MDD. Objective: To test whether low doses of the NMDA-receptor partial-agonist, D-cycloserine, would enhance intermittent TBS (iTBS) treatment outcomes in MDD. Design, Setting, and Participants: This was a single-site 4-week, double-blind, placebo-controlled, randomized clinical trial conducted from November 6, 2019, to December 24, 2020, including 50 participants with MDD. Participants were recruited via advertisements and referral. Inclusion criteria were as follows: age 18 to 65 years with a primary diagnosis of MDD, a major depressive episode with score of 18 or more on the 17-item Hamilton Depression Rating Scale, a Young Mania Rating Scale score of 8 or less, and normal blood work (including complete blood cell count, electrolytes, liver function tests, and creatinine level). Interventions: Participants were randomly assigned 1:1 to either iTBS plus placebo or iTBS plus D-cycloserine (100 mg) for the first 2 weeks followed by iTBS without an adjunct for weeks 3 and 4. Main Outcomes and Measures: The primary outcome was change in depressive symptoms as measured by the Montgomery-Åsberg Depression Rating Scale (MADRS) at the conclusion of treatment. Secondary outcomes included clinical response, clinical remission, and Clinical Global Impression (CGI) scores. Results: A total of 50 participants (mean SD age, 40.8 13.4 years; 31 female 62%) were randomly assigned to treatment groups: iTBS plus placebo (mean SD baseline score, 30.3 4.2) and iTBS plus D-cycloserine (mean SD baseline score, 30.4 4.5). The iTBS plus D-cycloserine group had greater improvements in MADRS scores compared with the iTBS plus placebo group (mean difference, -6.15; 95% CI, -2.43 to -9.88; Hedges g = 0.99; 95% CI, 0.34-1.62). Rates of clinical response were higher in the iTBS plus D-cycloserine group than in the iTBS plus placebo group (73.9% vs 29.3%), as were rates of clinical remission (39.1% vs 4.2%). This was reflected in lower CGI-severity ratings and greater CGI-improvement ratings. No serious adverse events occurred. Conclusions and Relevance: Findings from this clinical trial indicate that adjunctive D-cycloserine may be a promising strategy for enhancing transcranial magnetic stimulation treatment outcomes in MDD using iTBS requiring further investigation. Trial Registration: ClinicalTrials.gov Identifier: NCT03937596.