Lisdexamfetamine dimesylate augmentation for adults with major depressive disorder and inadequate response to antidepressant monotherapy: Results from 2 phase 3, multicenter, randomized, double-blind, placebo-controlled studies

Background: The efficacy, safety, and tolerability of lisdexamfetamine dimesylate (LDX) augmentation of antidepressant monotherapy in adults with major depressive disorder (MDD) from two phase 3 studies are reported.

Methods: Across study 1 (placebo, n=201; LDX, n=201) and study 2 (placebo, n=213; LDX, n=211), most participants (placebo and LDX) in the safety analysis set were female (study 1: 66.2% and 64.2%; study 2: 67.1% and 66.8%); mean±SD ages were 41.8±12.04 with placebo and 42.2±12.32 with LDX in study 1 and 42.6±11.41 with placebo and 42.0±11.63 with LDX in study 2. Participants (18-65 y) had DSM-IV-TR-diagnosed MDD and lead-in baseline Montgomery-Åsberg Depression Rating Scale (MADRS) total scores ≥24. Eight-week antidepressant lead-in phases prospectively assessed antidepressant response. Then, 8 weeks of randomized (1:1), double-blind treatment with dose-optimized LDX (20-70mg) or placebo in participants exhibiting inadequate antidepressant monotherapy responses (augmentation baseline MADRS total scores ≥18 and <50% MADRS total score reductions from lead-in baseline to augmentation baseline) was initiated. The primary endpoint was MADRS total score change from augmentation baseline to week 16. Safety and tolerability measures included the occurrence of treatment-emergent adverse events (TEAEs).

Results: Least squares mean (95% CI) treatment differences (LDX-placebo) for MADRS total score changes from augmentation baseline to week 16 were not statistically significant in study 1 (0.1 [-1.7, 2.0], P=0.883) or study 2 (-0.5 [-2.3, 1.3], P=0.583). The only TEAE reported by >5% of LDX participants at twice the placebo rate in both studies was dry mouth.

Limitations: Limitations include the exclusion of participants with psychiatric comorbidities/active medical disorders, the inability to assess specific MDD symptom domains (eg, anhedonia, cognition) or subtypes, the use of telephone-based depression assessments, and the potential influence of placebo response.

Conclusion: Contrary to expectations, LDX augmentation was not superior to placebo in reducing depressive symptoms in individuals with MDD exhibiting inadequate responses to antidepressant monotherapy.