Open-Label Adjunctive Zonisamide in the Treatment of Bipolar Disorders: A Prospective Trial

Background: The response of 62 outpatients with DSM-IV bipolar disorders to open-label adjunctive zonisamide was evaluated in a prospective 8-week acute trial, followed by a 48-week continuation trial, conducted from June 2001 through May 2002.

Method: During the acute trial, response to zonisamide was assessed weekly for the first 4 weeks and every 2 weeks for the second 4 weeks with the Clinical Global Impressions scale modified for bipolar illness (CGI-BP), the Young Mania Rating Scale (YMRS), and the Inventory for Depressive Symptomatology (IDS). During the continuation trial, patients were assessed with these scales every 4 weeks. Patients’ weights and side effects were also evaluated. Outcome measures were analyzed with repeated-measures analyses of variance.

Results: Patients with manic symptoms at study entry (N = 34) displayed significant reductions in CGI-BP-Mania Severity and YMRS scores in the acute and continuation (N = 19) trials (p values < .0001 and < .001, respectively). Patients with depressive symptoms at study entry (N = 22) showed significant decreases in CGI-BP-Depression Severity and IDS scores in the acute trial (p values < .001 and < .05, respectively), but only 9 patients entered the continuation trial. Among these 9 patients, maintenance of antidepressant response was mostly maintained. Initially euthymic patients (N = 6) showed no change in any rating scale scores acutely, but 2 of 4 patients who entered the continuation trial developed depressive symptoms. The 62 patients as a group showed significant weight loss in both trials (p values < .001). However, 20 patients (32%) discontinued zonisamide for worsening mood symptoms.

Conclusion: Adjunctive zonisamide was associated with beneficial effects on mood and body weight in some patients with bipolar disorders, but was also associated with a high discontinuation rate due to worsening mood symptoms. Double-blind, placebo-controlled studies are necessary to determine zonisamide’s thymoleptic properties, if any, in bipolar disorders.