Memantine for the Treatment of Primary Negative Symptoms in Schizophrenia: A Meta-analysis of Randomized Controlled Trials.

Background: Memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist with favorable safety and side effect profiles. There is a growing body of evidence for memantine as an adjunctive therapy for the positive, negative, and cognitive symptoms of schizophrenia.

Objective: This meta-analysis examined the efficacy of memantine as an add-on to treatment with antipsychotic(s) for the primary negative symptoms (PNS) of schizophrenia.

Methods: We followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and searched for relevant publications in PubMed, Cochrane Library, PsycINFO, Embase, and China Journal Net databases from inception using the following search terms: memantine, schizophrenia, randomized controlled trials (RCTs), RCT, and clinical trial. Searches were limited to English- and Chinese-language articles to date. Standardized mean differences (SMDs) with 95% confidence intervals were calculated using RevMan 5.4 to assess the effect size. Risk of bias was assessed using RoB 2.0.

Results: In total, 13 RCTs were identified (N = 681). Memantine was superior to placebo in treating negative symptoms, with an SMD of 0.79 (p = 0.0001, N = 631, 12 RCTs). Analysis of three studies whose corresponding authors provided original datasets showed an SMD of 2.16 (p = 0.25, N = 97) after adjusting for change in psychosis, depression, and extrapyramidal symptoms, suggesting that memantine is efficacious in treating PNS. Additionally, cognitive testing significantly improved, with an SMD of 0.66 (p = 0.0001, N = 395, eight RCTs). Positive symptoms were not significantly improved (SMD = 0.24, p = 0.1, N = 631, 12 RCTs).

Conclusions: To our knowledge, this is the first study showing a large effect size for treating PNS with memantine. Although statistical significance was not reached because of the small sample size (N = 97), the results were as expected because drugs such as memantine that act at NMDA receptors are unlikely to be effective as stand-alone treatments. Future RCTs should evaluate NMDAergic drugs in combination with complementary medications to optimize therapeutic effects for all three domains of schizophrenia psychopathology.