Moderators of antidepressant augmentation versus switch in the OPTIMUM randomised controlled trial

Older adults with treatment-resistant depression (TRD) benefit more from treatment augmentation than switching. It is useful to identify moderators that influence these treatment strategies for personalised medicine.

Our objective was to test whether age, executive dysfunction, comorbid medical burden, comorbid anxiety or the number of previous adequate antidepressant trials could moderate the superiority of augmentation over switching. A significant moderator would influence the differential effect of augmentation versus switching on treatment outcomes.

We performed a preplanned moderation analysis of data from the Optimizing Outcomes of Treatment-Resistant Depression in Older Adults (OPTIMUM) randomised controlled trial (N = 742). Participants were 60 years old or older with TRD. Participants were either (a) randomised to antidepressant augmentation with aripiprazole (2.5-15 mg), bupropion (150-450 mg) or lithium (target serum drug level 0.6 mmol/L) or (b) switched to bupropion (150-450 mg) or nortriptyline (target serum drug level 80-120 ng/mL). Treatment duration was 10 weeks. The two main outcomes of this analysis were (a) symptom improvement, defined as change in Montgomery-Asberg Depression Rating Scale (MADRS) scores from baseline to week 10 and (b) remission, defined as MADRS score of 10 or less at week 10.

Of the 742 participants, 480 were randomised to augmentation and 262 to switching. The number of adequate previous antidepressant trials was a significant moderator of depression symptom improvement (b = -1.6, t = -2.1, P = 0.033, 95% CI [-3.0, -0.1], where b is the coefficient of the relationship (i.e. effect size), and t is the t-statistic for that coefficient associated with the P-value). The effect was similar across all augmentation strategies. No other putative moderators were significant.

Augmenting was superior to switching antidepressants only in older patients with fewer than three previous antidepressant trials. This suggests that other intervention strategies should be considered following three or more trials.