A systematic review and meta-analysis of the evidence base for add-on treatment for patients with major depressive disorder who have not responded to antidepressant treatment: A European perspective

Previous comparative reviews of add-on therapies for patients with major depressive disorder (MDD) with an inadequate response to antidepressants have not used meta-analytic techniques to compare different drug classes and have included non-licensed therapies. This meta-analysis reviewed all published peer-reviewed evidence for the efficacy of EU-licensed therapies in patients with MDD and an inadequate response to antidepressant monotherapy. Papers concerning randomized clinical trials (RCTs) were identified using criteria from the Cochrane Handbook for Systematic Reviews of Interventions. Add-on therapies reviewed were antidepressants, quetiapine XR, lithium, and S-adenosyl-l-methionine (SAMe). Seven RCTs that reported response and remission in a way that allowed quantitative analysis were included in this meta-analysis. Comparison of the different drug classes indicated that most interventions had similar efficacy. The likelihood of response was significantly greater with SAMe versus placebo and lithium and with quetiapine XR versus placebo. Most add-on interventions demonstrated comparable efficacy in patients with MDD and an inadequate response to initial antidepressants. However, there is currently a paucity of high-quality data regarding the use of add-on treatments in patients with MDD who are inadequate responders to antidepressants, with quetiapine XR presenting the most comprehensive evidence base to date.