Polarity index of pharmacological agents used for maintenance treatment of bipolar disorder.

Over one half of bipolar patients have been reported to be more prone to either depressive or manic relapses. This study aimed to define profiles of drugs used for maintenance treatment of bipolar disorder (BD) by the means of Polarity Index. Polarity Index is a new metric indicating the relative antimanic versus antidepressive preventive efficacy of drugs. Polarity Index was retrieved by calculating Number Needed to Treat (NNT) for prevention of depression and NNT for prevention of mania ratio, as emerging from the results of randomized placebo-controlled trials. Included trials were randomized and double blind, with a minimal duration of 24 weeks, assessing effectiveness of a mood stabilizer or antipsychotic drug alone or in combination with a mood stabilizing agent versus a placebo comparator in BD maintenance treatment. Polarity Index value above 1.0 indicates a relative greater antimanic prophylactic efficacy, number below 1.0 a relative greater antidepressive efficacy. The polarity index for the drugs used in maintenance therapy for bipolar disorder was 12.09 for risperidone, 4.38 for aripiprazole, 3.91 for ziprasidone, 2.98 for olanzapine, 1.39 for lithium, 1.14 for quetiapine, and 0.40 for lamotrigine. Polarity index of valproate and oxcarbazepine may not be reliable due to the failure of their maintenance trials. The polarity index provides a measure of how much antidepressant versus antimanic a drug is in bipolar disorder prophylaxis, and may guide the choice of maintenance therapy in bipolar patients.