A randomised, placebo-controlled 24-week study evaluating adjunctive brexpiprazole in patients with major depressive disorder.

Objective: To evaluate brexpiprazole adjunctive to antidepressant therapies (ADTs) as maintenance treatment in patients with major depressive disorder with inadequate response to ADT, utilising a novel study design.

Methods: The study comprised an 8-week prospective treatment period with open-label ADT with double-blind placebo treatment and a 24-week randomised treatment period. Investigators and patients were blinded to treatment periods, randomisation criteria, and timing of randomisation. Patients with early response to open-label ADT were withdrawn at Week 6. Patients fulfilling criteria for inadequate response were randomised to ADT+brexpiprazole 1-3 mg/day, or ADT+placebo. The primary endpoint was full remission: Montgomery-Åsberg Depression Rating Scale (MADRS) total score ≤10 and ≥50% decrease from randomisation (i.e. baseline) in MADRS total score for at least 8 consecutive weeks.

Results: The primary efficacy analysis failed to show a statistically significant difference between the proportions of patients on ADT+brexpiprazole (21.4%) and ADT+placebo (24.9%) achieving full remission; odds ratio: 0.83; p=0.2641. The secondary endpoint of change from baseline to Week 6 in MADRS total score showed no difference between ADT+brexpiprazole and ADT+placebo (-0.4; p=0.3259). The most frequent treatment-emergent adverse event (TEAE) in patients receiving ADT+brexpiprazole was weight increased (9.5% vs. 5.0% in ADT+placebo). The incidence of TEAEs leading to withdrawal in the randomised treatment period was 6.3% in the ADT+brexpiprazole group and 3.4% in the ADT+placebo group.

Conclusion: Adjunctive brexpiprazole did not differentiate from ADT+placebo on the primary endpoint of full remission. A number of design elements in this previously untried study design may have contributed to the study result. Brexpiprazole was well tolerated.