Objectives: Chronic inflammation and neuroprogression underlie bipolar disorder (BP) and associated cognitive deficits. Memantine (MM) exerts neuroprotective effects by reducing neuroinflammation. Therefore, we investigated whether add-on low-dose MM (5 mg/day) in BP-II patients may improve cognition and inflammation. Methods: We combined two 12-week randomized, double-blind, placebo-controlled studies (NCT 01188148 and NCT 03039842) for analysis. Each participant was allocated to the MM or placebo group. Symptom severity, neuropsychological tests, and the cytokine plasma levels [tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), interleukin-8 (IL-8), transforming growth factor-β1 (TGF-β1), and brain-derived neurotrophic factor (BDNF)] were evaluated at baseline and endpoint. A subgroup analysis of middle- to old-aged BP-II patients was also performed. Results: We recruited 155 BP-II patients (23 of which were middle- to old-aged) for the MM group and 170 patients (20 of which were middle- to old-aged) for the placebo group. Add-on MM did not result in significant improvements in cognitive functions in all BP-II patients, but a group difference in TNF-α levels was found in the MM group (P=0.04). Specifically, in middle- to old-aged BP-II patients, there was a significant time and group interaction effect on omission T-scores, hit reaction time T-scores, and hit reaction time standard error T-scores on continuous performance tests (CPTs) in the MM group (P=0.007, 0.02, and 0.01, respectively), and a decrease in plasma TNF-α levels (P=0.04). Limitations: The sample size of middle- to old-aged BP-II patients were limited. Conclusion: Add-on MM may attenuate inflammation in BP-II and improve cognition in middle- to old-aged BP-II patients.
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