Lithium in the treatment of acute bipolar depression: A systematic review and meta-analysis

Objectives: To evaluate lithium in the treatment of acute bipolar depression.

Methods: We conducted a systematic literature review for: 1) cross-over or parallel-group design studies comparing lithium response in bipolar versus unipolar depressed patients, and 2) parallel group studies of bipolar depressed patients comparing lithium versus placebo or other psychotropics. Meta-analyses using response rate as the primary outcome were conducted to evaluate lithium's efficacy.

Results: The literature search yielded 947 records. Ultimately, 17 studies were included, totaling 1545 patients, including 676 who received lithium. The overall summary effects reveal that there were no statistically significant differences between lithium versus antidepressants or placebo, however, lithium performed numerically worse than antidepressants (RR = 0.61; 95%CI, 0.37-1.02; p = 0.06) but better than placebo (RR = 1.18; 95%CI, 0.99-1.41; p = 0.07). The specificity of lithium for bipolar versus unipolar depression was not supported in the primary analysis of all trials, though an analysis limited to double-blinded, monotherapy, cross-over studies revealed a statistically significant result supporting lithium's efficacy for those with bipolar depression.

Limitations: Limitations include study selection rules, the use of response rates rather than remission rates or continuous score outcomes, and the small number of studies included in each meta-analysis.

Conclusions: These meta-analyses do not support lithium as a first-line treatment for acute bipolar depression. However, the bipolar vs. unipolar sensitivity analysis and the modest, though non-significant advantage over placebo suggest lithium may still be a viable treatment option. Larger and more rigorously-designed studies are needed to determine lithium's full range of efficacy relative to placebo and other psychotropics.