Lamotrigine potentiates the antidepressant effects of quetiapine in bipolar depression
At the 2015 meeting of the International Society for Bipolar Disorders, researcher John Geddes presented an important study showing in inadequate responders to quetiapine that compared to adding placebo, adding the anticonvulsant lamotrigine to their treatment improved depression rapidly and lastingly. Some psychiatrists have been prescribing this combination to patients for some time, but this is the first formal clinical trial documenting its efficacy. The article was published online in December in the journal Lancet Psychiatry.
Researcher Guy Goodwin described details of the study, called CEQUEL, at the meeting. It included 202 patients with bipolar I or II disorder who required treatment for a depressive episode. Participants who did not respond completely to 14 days of treatment with quetiapine were prescribed either an additional dose of lamotrigine or a placebo. Lamotrigine was very slowly titrated up to maximum doses of 200mg/day. Its antidepressant effects were striking. They began early and persisted for 50 weeks. (The published article covers only the first 12 weeks.) Response rates for the combination of quetiapine and lamotrigine were 52%, compared to 22% for quetiapine alone. Remission rates were 35% for quetiapine and lamotrigine and 12% for quetiapine alone.
Folic acid interaction
Another part of the study assessed whether folic acid supplements could improve outcomes, but in fact they did the opposite, reversing the benefits of adding lamotrigine. Geddes did not have an explanation for why this might be the case. Lamotrigine can inhibit folate metabolism, and it had been thought that adding folate would be useful. Until further data are gathered on folate augmentation in patients taking the combination of lamotrigine and quetiapine, folate should be used cautiously if at all in these patients.
Possible combination with lithium
In Goodwin’s talk, he also noted lithium’s potential to lower suicide rates, premature mortality, and cognitive impairment, and to increase hippocampal and cortical volume.
Since lamotrigine was shown to potentiate the antidepressant effects of lithium in a study by Van der Loos and colleagues, and quetiapine is approved by the Food and Drug Administration for the prevention of depression as an adjunct to lithium (or valproate), there might be theoretical acute and long-term benefits to combining the three: lithium, quetiapine, and lamotrigine.
