Systematic Review and Meta-Analysis: Dose-Response Relationship of Selective Serotonin Reuptake Inhibitors in Major Depressive Disorder

Abstract

Objective Previous studies suggested that the treatment response to Selective-Serotonin Reuptake Inhibitors (SSRIs) in Major Depressive Disorder (MDD) follows a flat response curve within the therapeutic dose range. Our study was designed to clarify the relationship between dosage and treatment response in MDD. Methods We searched PubMed for randomized placebo-controlled trials examining the efficacy of SSRIs for treating adults with MDD. Trials were also required to assess improvement in depression severity at multiple time points. Additional data was collected on treatment response and all cause and side effect-related discontinuation. All medication doses were transformed into imipramine equivalent doses. The longitudinal data was analyzed with a mixed regression model. Endpoint and tolerability analyses were analyzed using meta-regression and stratified subgroup analysis by predefined SSRI dose categories in order to assess the effect of SSRI dosing on the efficacy and tolerability of SSRIs for MDD. Results We included 40 studies involving 10,039 participants.. Longitudinal modeling [dose × time interaction=0.0007(95%CI:0.0001–0.0013;p=0.0196)] and endpoint analysis (meta-regression β=0.00053,95%CI:0.00018–0.00088,z=2.98,p=0.0029) demonstrated a small, but statistically significant positive association between SSRI dose and efficacy. Higher doses of SSRIs were associated with an increased likelihood of dropouts due to side-effects (meta-regression β=0.00207,95%CI:0.00071–0.00342,z=2.98,p=0.003) and decreased likelihood of all-cause dropout (meta-regression β=−0.00093,95% CI−0.00165–(−0.00021),z=−2.54,p=0.01). Conclusions Higher doses of SSRIs appear slightly more effective in MDD. This benefit appears to plateau around 250mg of imipramine equivalents (50mg of fluoxetine). The slightly increased benefits of SSRIs at higher doses are somewhat offset by decreased tolerability at high doses.

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