Differential Efficacy of Olanzapine and Lithium in Preventing Manic or Mixed Recurrence in Patients With Bipolar I Disorder Based on Number of Previous Manic or Mixed Episodes

Introduction: Bipolar disorder outcome worsens as number of manic episodes increases, suggesting that prevention of recurrent episodes early during the disorder could improve patient prognosis. We investigated treatment efficacy in prevention of mood episodes in patients subgrouped by number of prior manic episodes.

Method: This study was a post hoc analysis of data from a multicenter, double-blind, 12-month clinical trial of relapse/recurrence in 431 initially euthymic patients with at least 2 prior manic/mixed episodes and a DSM-IV diagnosis of bipolar I disorder randomly assigned to olanzapine (5-20 mg/day) or lithium (serum concentration 0.6 to 1.2 mEq/L). Data were collected between August 1999 and June 2002. Patients were subcategorized by illness stage according to number of prior manic/mixed episodes-early stage: 2 prior episodes (N = 53, lithium; N = 48, olanzapine), intermediate stage: 3 to 5 prior episodes (N = 80, lithium; N = 98, olanzapine), and later stage: more than 5 prior episodes (N = 81, lithium; N = 71, olanzapine)-and were evaluated for rates of relapse/recurrence.

Results: There were significant effects for treatment (p < .001) and illness stage (p = .006) but no significant interaction (p = .107) on rate of manic/mixed relapse/recurrence. Rates of manic/mixed relapse/recurrence for olanzapine versus lithium were 2.1% versus 26.4% (p = .008), 13.3% versus 23.8% (p = .073), and 23.9% versus 33.3% (p = .204) for early-, intermediate-, and later-stage groups, respectively. There was no significant effect for treatment (p = .096) or illness stage (p = .731) for depressive relapse/recurrence.

Conclusions: Early-stage (but not intermediate-or later-stage) patients had a significantly lower rate of relapse/recurrence of manic/mixed episodes with olanzapine compared to lithium. Thus, olanzapine maintenance therapy may be particularly effective early in the course of bipolar illness.