In a recent placebo-controlled, double blind crossover trial (n = 52), we found significant beneficial effects on memory (d = 0.30) and negative symptoms (d = 0.29) after 12 weeks memantine augmentation in patients with clozapine-refractory schizophrenia.

In this open-label 1 year extension study, we report the long-term effects and tolerability of memantine add-on therapy to clozapine.

Completers of the first trial who experienced beneficial effects during 12 weeks of memantine treatment received memantine for one year. Primary endpoints were memory and executive function using the Cambridge neuropsychological test automated battery (CANTAB), the Positive and Negative Syndrome Scale (PANSS), and the Clinical Global Impression Severity Scale (CGI-S).

Of 31 RCT completers who experienced beneficial effects from memantine, 24 received memantine for one year. The small improvement in memory found in the memantine condition in the placebo-controlled trial remained stable in the extension study. Executive function did not improve. After 26 weeks of memantine add-on therapy to clozapine, PANSS negative symptoms (r = 0.53), PANSS positive symptoms (r = 0.50), and PANSS total symptoms (r = 0.54) significantly improved. Even further significant improvement in all these measures was observed between 26 weeks and 52 weeks memantine, with effect sizes varying from 0.39 to 0.51. CGI-S showed a non-significant moderate improvement at 26 weeks (r = 0.36) and 52 weeks (r = 0.34). Memantine was well tolerated without serious adverse effects.

In the one-year extension phase, the favorable effect of adjunctive memantine on memory was sustained and we observed further improvement of positive, negative and overall symptoms of schizophrenia.

P.F.J.S. reports personal fees from H. Lundbeck A/S, outside the submitted work and he is a board member of the Dutch Clozapine Collaboration Group. L.d.H., has received investigator-led research grants or recompense for presenting his research from Eli Lilly, Bristol-Myers Squibb, Janssen-Cilag and AstraZeneca.