Number needed to treat analyses of drugs used for maintenance treatment of bipolar disorder.
Due to the episodic and chronic nature of bipolar disorder (BD), maintenance therapy represents a critical part of treatment; however, there is a paucity of studies comparing effectiveness of available long-term treatments. The aim of this study is to determine and compare the efficacy of pharmacological treatments for maintenance treatment of BD by means of the number needed to treat (NNT). The efficacy of drugs used for maintenance treatment of BD, as emerging from the results of randomized controlled trials, was assessed using the size effect measure of NNT. PubMed searches were conducted on English-language articles published until May 2010 using the search terms "bipolar disorder," "mania," "mixed episode," or "bipolar depression," cross-referenced with trial characteristic search phrases and generic names of medications. The search was supplemented by manually reviewing reference lists from identified publications. In 15 studies, aripiprazole, olanzapine, quetiapine, risperidone long-acting injection, lithium, lamotrigine, and divalproex proved effectiveness in terms of NNTs (≥ 10% advantage over placebo) for prevention of relapse into any mood episode. Quetiapine, lithium, risperidone long-acting injection, aripiprazole, and olanzapine are effective in manic recurrence prevention. Lamotrigine, quetiapine, and lithium present significant NNTs for prevention of depressive relapses. All of the pharmacological agents assessed were effective in the prevention of any kind of mood episode; however, different efficacy profiles were found for prevention of manic and/or depressive relapses. The comparison of NNT values of the available agents may represent a useful tool in clinical settings, in order to facilitate implementation of long-term pharmacological interventions in patients with BD.