Does lamotrigine augment clozapine?

Many of the patients referred to B.C psychosis Program are on clozapine or have received it in the past, and many have had a limited response. Clozapine-resistance is a big challenge for psychiatrists who manage chronic psychosis, and a recent quantitative review of clozapine augmentation strategies provides little guidance or solace. Stefan Leucht and colleagues examined randomized, masked, placebo-controlled studies

of at least two weeks duration in which another drug was added following at least four weeks of  clozapine therapy. Whenever possible, they used intention-to-treat data to calculate effect size.

The studies involved a range of medications including antidepressants, antipsychotics, glutamatergic agents, and antiepileptics. Lamotrigine is particularly of interest because Tiihonen’s group performed a meta-analysis in 2009 based on five studies that showed a significant effect for augmentation of clozapine. This group obtained unpublished data from studies that looked at lamotrigine added to a variety of antipsychotics, and intention-to-treat outcomes from the trial by Zocali, the largest study to date with 30 subjects on active therapy. Based on the 2009 meta-analysis, Goff commented that “the addition of lamotrigine in patients who remain symptomatic despite adequate clozapine treatment represents the most promising treatment option currently available.”

Although Tiihonen et al. found insignificant heterogeneity, Leucht et al. did find heterogeneity and concluded that the Zocali study was an outlier. They therefore excluded it from their final analysis. This is the crucial difference between the two meta-analyses and the reason for the sharply divergent conclusions. Four studies of lamotrigine augmentation are negative and one is positive. A closer look reveals that the Zocali trial was 24 weeks in duration, whereas the other trials were 10 to 14 weeks; could this be a crucial difference? Goff is still correct, and rather than throw lamotrigine overboard, we need a replication trial lasting 24 or 30 weeks. We know that the benefits of clozapine may take many months to be fully evident, so we should not expect that clozapine augmentation to be a quick affair.

As for other findings of the Leucht meta-analysis, sulpiride augmentation showed significant impact on both positive and negative symptoms, and citalopram showed significant impact on negative symptoms, but the findings are based on one trial each. A trial of an experimental glutamatergic agent showed a signal. This leaves us with few clear optins but some direction for further research.

References

Sommer IE, Begemann MJ, Temmerman A, Leucht S. Pharmacological augmentation strategies for schizophrenia patients with insufficient response to clozapine: a quantitative literature review. Schizophr Bull. Mar 21 2011; Epub ahead of print; doi:10.1093/schbul/sbr004

Tiihonen J, Wahlbeck K, Kiviniemi V. The efficacy of lamotrigine in clozapine-resistant schizophrenia: A systematic review and meta-analysis. Schizophr Res. 2009;109:10–14.

Goff DC. Review: lamotrigine may be an effective treatment for clozapine resistant schizophrenia. Evid Based Mental Health. 2009;12:111.

Zoccali R,Muscatello MR,Bruno A, Cambria R, et al. The effect of lamotrigine augmentation of clozapine in a sample of treatment-resistant schizophrenic patients: a double-blind, placebo-controlled study. Schizophr Res. 2007;93:109–116.

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