Polarity index helps focus bipolar treatment
By Lucy Piper, Senior medwireNews Reporter
25 July 2013
Acta Psychiatr Scand 2013; Advance online publication

medwireNews: Study findings confirm the benefit of identifying the polarity index of patients with bipolar disorder in order to optimize their treatment.

The polarity index is a numeric expression used to determine the prophylactic efficacy profile of drugs used to treat bipolar disorders, the researchers explain. It is based on the ratio of the number needed to treat (NNT) for prevention of depressive episodes and the NNT for mania prevention.

Drugs with a polarity index superior to 1 have stronger antimanic versus antidepressant prophylactic properties, while those with a polarity index inferior to 1 have greater antidepressant treatment potential.

When they applied this metric to the drugs prescribed to 257 bipolar disorder patients from a tertiary center, of whom 143 (55.6%) were classified as having a depressive polarity and 114 (44.4%) a manic polarity, researchers Eduard Vieta (University of Barcelona, Spain) and colleagues found that it was in accordance with the patients’ predominant polarity.

Specifically, the average polarity index of all prescribed antipsychotics and mood stabilizers was higher in the predominantly manic patients than in the predominantly depressive patients, at 3.68 versus 2.22.

This indicates that, for patients who were predominantly manic, “clinicians chose a treatment regimen with stronger antimanic prophylactic action, than [depressive predominant polarity patients],” the researchers note in Acta Psychiatrica Scandinavica.

The results were the same when antipsychotic and mood stabilizers were assessed separately.

Vieta et al therefore believe that “the polarity index may be helpful as a tool to assess the quality of maintenance prescription for bipolar patients.”

They also found several clinical differences between the two groups. Manic predominance was associated with being male and younger overall as well as at illness onset and first hospitalization, having higher rates of hospitalization, and the presence of substance abuse and psychotic symptoms.

By contrast, depressive predominance was associated with bipolar II disorder, stressful life events preceding illness onset, and more suicide attempts and melancholic features.

The team concludes that, given these important clinical differences , the need for a differentiated treatment approach is “justified,” and the polarity index metric may help in ensuring the best approach.

medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013

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