With modulating dopamine as the primary pharmacotherapeutic option to treat schizophrenia, we are left unable to adequately treat at least 30% of our patients, Dr. Christoph Correll told the audience at the 2016 Pacific Psychopharmacology Conference in Vancouver. The evidence for combining dopamine antagonists, whether first- or second-generation antipsychotics, is not favorable according to a meta-analysis he described which is in review for publication. When only high-quality studies were included, which involved 14 trials with 938 subjects, the evidence for combining antipsychotics melted to nothing. Although it makes sense that using two medications with the essentially the same mechanism of action would not be synergistic, many practitioners nevertheless do just that.
Dr. Correll, who is Professor of Psychiatry at Hofstra Northwell School of Medicine and Medical Director of the Recognition and Prevention Program at the Zucker Hillside Hospital in Queens, New York, said that adding agents with a different mechanism of action may be more promising. Topirimate acts to inhibit activity in the glutamate-NMDA receptor complex and is approved as an anticonvulsant. It also counters the weight gain of psychotropic medications by reducing appetite and enhancing insulin sensitivity. He and six coauthors have recently published a meta-analysis of 16 randomized, controlled trials including a total of 934 patients who received topirimate adjunctive to antipsychotic therapy; outcome data included PANSS or BPRS total scores and body weight, and secondary outcomes included positive and negative symptoms and various metabolic measures including waist circumference and serum glucose.
The benefit for augmentation was significant as measured by total PANSS or BPRS for the entire group, and sensitivity analyses showed it held true with a dose of 150 mg per day or less, in first and multi-episode patients, and either with clozapine or non-clozapine antipsychotics. The effect was independently significant for positive and for negative symptoms. Topirimate was associated with a significant reduction in weight with a mean reduction of 2.75 kg; other metabolic measures were unchanged except for significant reduction in serum triglycerides and fasting insulin. Although discontinuation for adverse effects or inefficacy did not differ with topirimate or placebo, notable adverse effects of topirimate included concentration problems and paresthesias.
These studies were all short-term with a mean duration of 11.8 weeks, a problem with many clinical trials in psychiatry given that schizophrenia is a chronic disorder and patients remain on medication for months to years. Cognitive problems including word-finding difficulty are a known effect of topirimate, and in an illness in which cognitive impairment is inherent, this could be a major liability. Longer-term effects on cognition, metabolic outcomes and psychosis are needed. Will topirimate be the NMDA-modulating treatment that makes a difference or end up like lamotrigine, abandoned after a brief dalliance?
Zheng W, Xiang Y-T, Xiang Y-Q, Li X-B, Ungvari GS, Chiu HFK, Correll CU. Efficacy and safety of adjunctive topiramate for schizophrenia: a meta-analysis of randomized controlled trials. Acta Psychiatr Scand. 2016:1–14. Published online 1 Sep 2016. Abstract