Therapeutic Window of Lamotrigine for Mood Disorders: a Naturalistic Retrospective Study

Introduction: Lamotrigine is widely used for mood disorders including bipolar disorder and major depression, but its therapeutic levels have yet to be determined. This study was conducted to investigate the hypothesis that lamotrigine may have a therapeutic window for mood disorders.

Methods: 25 patients with mood disorders received lamotrigine for more than one year during which time plasma lamotrigine levels were measured at least once. Their mental state was retrospectively and regularly but blindly assessed using the Clinical Global Impression-Severity (CGI-S) scale. In order to investigate our hypothesis, we depicted the relationship between the last lamotrigine levels and the last CGI scores in 25 patients. If any, the potential therapeutic window was further investigated.

Results: The relationship between the last lamotrigine levels and the last CGI scores in the 25 patients indicated the presence of a therapeutic window of lamotrigine from 5 to 11 μg/mL. The repeated measures of ANOVA reached a significant tendency of the effects of lamotrigine levels within 5-11 μg/mL on better CGI-S scores, and the CGI-S scores at the last observation of the 15 patients whose lamotrigine levels were within 5-11 μg/mL were significantly better than those of 10 patients whose lamotrigine levels were not within 5-11 μg/mL.

Conclusion: These findings suggest that lamotrigine may have a therapeutic window for patients with mood disorder from 5 to 11 μg/mL.