No study to date has compared lithium and lamotrigine as maintenance mood stabilizers for bipolar II disorder. The aim of this study was to evaluate and compare these two medications in terms of their maintenance efficacy and side effect profile, thus evaluating their comparative cost/benefit profile.
Forty-four subjects with a newly diagnosed bipolar II disorder were randomly assigned to receive either lithium or lamotrigine treatment in a 20-week single-blinded study. Subjects received either slow-release lithium progressively up-titrated to achieve a serum level of 0.8 mEq/L, or lamotrigine increased progressively to a maintenance dose of 200 mg/d. Our primary outcome measure examined daily data on hypomanic and depressive symptoms. Secondary measures evaluated hypomanic and depressive symptom severity, global functioning, and global improvement in hypomanic and depressive symptoms.
We terminated the trial principally because of severe ongoing side effects experienced by many of those receiving lithium, and with additional concerns about initial severe side effects (including psychosis) experienced by several assigned to lamotrigine. Analyses of study completer data for 28 participants suggested comparable efficacy of both medications; however, lamotrigine had a distinctly lower rate of severe side effects across the study. We calculated that if study trends on outcome measures were valid, then an extremely large sample would be required to demonstrate superiority of either drug, thus making it unlikely that any such adequately powered study will be mounted in the future.
The small sample size limits any definitive conclusions, but our data suggest that lithium and lamotrigine are likely to have equal efficacy as mood stabilizers for those with a bipolar II condition but that, as maintenance treatments, lithium has more distinctive side effects.