Minocycline as adjunctive treatment for major depressive disorder: Pooled data from two randomized controlled trials

Background: Randomized controlled clinical trials that have investigated minocycline as an adjunctive treatment for major depressive disorder have proved promising. Data from two studies were pooled to evaluate more definitively whether the addition of minocycline to standard treatment for major depressive disorder leads to an improvement of depressive symptoms when compared with placebo. Methods: Both studies were multi-site, double-blinded, placebo-controlled trials of minocycline 200 mg/day added to treatment as usual during a 12-week period. The primary outcome measure was change in depressive symptoms (Montgomery–Asberg Depression Rating Scale in Dean et al. and Hamilton Depression Rating Scale in Husain et al.). Secondary outcomes were change in depression severity (Montgomery–Asberg Depression Rating Scale for Dean et al. and 9-item Patient Health Questionnaire in Husain et al.), anxiety severity (Hamilton Anxiety Rating Scale in Dean et al. and Generalized Anxiety Disorder 7-item scale in Husain et al.) and functional status, which were also evaluated as potential mediators on the primary outcome. Results: A total of 112 participants were included in the pooled data (Dean et al., n = 71; Husain et al., n = 41). A significant change from baseline to week 12 was noted in depressive symptoms – differential change (Placebo vs Minocycline): 9.0, 95% confidence interval = [4.2, 13.9], Cohen’s D (95% confidence interval): 0.71 [0.29, 1.14], p < 0.001 – anxiety severity – differential change (Placebo vs Minocycline): 0.38, confidence interval = [0.00, 0.75], Cohen’s D (95% confidence interval): 0.41 [0.00, 0.82], p = 0.050) and functional status – differential change (Placebo vs Minocycline): 1.0, 95% confidence interval = [0.4, 1.5], Cohen’s D (95% confidence interval): 0.76 [0.34, 1.19], p = 0.001). Duration of illness, current use of benzodiazepine and pain medication were identified as moderators, whereas functional status as a mediator/predictor. Conclusion: The improvement of depressive symptoms, anxiety severity and functional status is promising and suggests that minocycline has potential as an adjunctive treatment for major depressive disorder. However, further studies are warranted to confirm therapeutic effects of minocycline in major depressive disorder. Trial registrations: NCT02263872, registered October 2014, and ACTRN12612000283875, registered March 2012.