Background: Dextromethorphan is an over-the-counter antitussive agent that may be a rapidly acting treatment for bipolar depression. Like ketamine, it is an NMDA receptor antagonist.
Methods: We conducted a retrospective chart review of depressed patients with treatment resistant bipolar II or bipolar NOS disorder who were treated with the combination of dextromethorphan 20 mg and quinidine 10 mg (DMQ). One pill of DMQ taken once or twice a day was added to participants׳ drug regimen. No changes were made to the pre-existing drug regimen during the course of treatment with DMQ. The primary outcome measure was the Clinical Global Impression-Improvement (CGI-I) score after 90 days of treatment.
Results: Seventy-seven participants met the inclusion criteria. All had been experiencing depressive symptoms for at least two years, and the mean number of failed medication trials was 21.2. The average CGI-I score at day 90 was 1.66 (1=slightly improved, 2=much improved). Some patients reported improvement within 1-2 days of starting DMQ. Nineteen patients discontinued treatment due to adverse effects, chiefly nausea.
Limitations: Because this was a retrospective chart review with no control group, conclusions about causation cannot be made. Nevertheless, the duration of depressive symptoms prior to starting DMQ makes spontaneous recovery less likely.
Conclusions: DMQ, an NMDA antagonist, may be effective in the treatment of bipolar depression. Because its putative mechanism does not depend on the monoaminergic system, it may be appropriate for patients who have not responded to other medications. Unlike ketamine, DMQ does not require i.v. administration.
Keywords: Bipolar II; Bipolar NOS; Dextromethorphan; N-methyl-d-aspartate receptor; NMDA; Quinidine.
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