More evidence on additive antipsychotic effect of adjunctive mirtazapine in schizophrenia: an extension phase of a randomized controlled trial

Abstract

Objective: Adjunctive mirtazapine improved negative symptoms of schizophrenia in several studies. Recently, we found an improvement also in positive symptoms when mirtazapine was added to first generation antipsychotics (FGAs) in a 6 week randomized controlled trial (RCT). The short duration of that trial was its limitation. This study aimed to explore whether longer treatment is worthwhile.

Method: Completers of the RCT (n = 39) received open-label add-on mirtazapine for additional 6 weeks. The Positive and Negative Syndrome Scale (PANSS) total score (primary outcome) and several other clinical parameters were measured prospectively.

Results: During the open-label phase, significant improvement was achieved in all parameters, with an effect size of 0.94 (CI 95% = 0.45-1.43) on the primary outcome and an impressive additive antipsychotic effect. Patients who received mirtazapine during both phases demonstrated greater improvement in positive symptoms (29.6% versus 21.2%, p = 0.027) than those who received mirtazapine during open-label extension phase only.

Conclusions: These findings support our previous data on the additive antipsychotic effect of mirtazapine in FGAs-treated schizophrenia. Mirtazapine may be effective in other symptom domains, too. Longer duration of mirtazapine treatment may yield additional benefits. If these results will be confirmed in larger studies, add-on mirtazapine may become a feasible option in difficult-to-treat schizophrenia.