Minocycline for negative symptoms of schizophrenia and possible mechanistic actions: the BeneMin RCT

Abstract

Background In a previous trial we reported that the neuroprotective, anti-inflammatory antibiotic minocycline lessened the negative symptoms of schizophrenia compared with placebo over 1 year. The BeneMin study aimed to replicate this benefit and to determine whether or not there was associated preservation of grey matter, reduction in circulating inflammatory cytokines and enhancement of cognition. Objectives To determine the efficacy of minocycline on the negative symptoms of schizophrenia and the mechanistic role of neuroprotective, anti-inflammatory and cognitive enhancing actions. Methods Two hundred and seven patients with a current research diagnosis of schizophrenia within 5 years of onset were randomised by a permuted blocks algorithm to minocycline (300 mg/day) or matching placebo as an adjunct to their continuing treatment. The primary efficacy outcome variable was the negative symptom subscale score from the Positive and Negative Syndrome Scales at 2, 6, 9 and 12 months. The primary mechanistic (biomarker) variables were (1) medial prefrontal grey matter volume (GMV), (2) circulating cytokine interleukin (IL) 6 concentration and (3) dorsolateral prefrontal cortex functional magnetic resonance imaging (fMRI) activations during performance of the N-back task. Movement disorder, side effects and treatment adherence were monitored throughout the study. Results Compared with placebo, the addition of minocycline had no effect on the severity of negative symptoms [treatment effect difference –0.186, 95% confidence interval (CI) –1.225 to 0.854] across the 2-, 6-, 9- and 12-month follow-up visits. None of the mechanistic biomarkers was influenced by minocycline: left GMV –91.2 (95% CI –303.8 to 121.4), IL-6 0.072 (95% CI –0.118 to 0.262) and N-back fMRI 0.66 (95% CI –1.53 to 0.20). There were no statistically significant treatment effects on any of the secondary outcomes and no group differences at baseline. Most measures were stable over the 12 months. Twenty-five out of the 29 serious adverse events were hospital admission for worsening psychiatric state, which affected 10 minocycline-treated participants and six placebo-treated participants.