Post hoc analysis of a randomised, placebo-controlled, active-reference 6-week study of brexpiprazole in acute...

We provide a closer look at the result of a randomised, placebo-controlled, active-reference (quetiapine XR), flexible-dose, 6-week study of brexpiprazole in schizophrenia, which did not meet its primary endpoint - change from baseline in Positive and Negative Syndrome Scale (PANSS) total score. We also investigate potential expectancy bias from the well-known side-effect profile of the active reference that could have affected the study outcome.

Pre-specified sensitivity analyses of the primary end point were performed using analysis of covariance (ANCOVA) last observation carried forward (LOCF) and observed cases (OC). Post hoc analyses of change from baseline in PANSS total score were performed using the mixed model for repeated measures approach with treatment groups split by having typical adverse events with potential for functional unblinding, for example, somnolence, increase in weight, dizziness, dry mouth and sedation.

Pre-specified sensitivity analyses showed separation from placebo for brexpiprazole at week 6: LOCF, ANCOVA: -4.3 [95% CI (-8.0, -0.5), p = 0.0254]. OC, ANCOVA: -3.9 [95% CI (-7.3, -0.5), p = 0.0260]. Patients treated with brexpiprazole experiencing typical adverse events with potential for functional unblinding before or at Week 2 had a least square (LS) mean PANSS change of -29.5 (improvement), with a difference in change from baseline to Week 6 in PANSS total score between brexpiprazole and placebo of -13.5 [95% CI (-23.1, -4.0), p = 0.0057], and those who did not had an LS mean change of -18.9 and a difference between brexpiprazole and placebo of -2.9 [95% CI (-7.2, 1.4), p = 0.1809].

Pre-specified sensitivity analyses showed separation from placebo for brexpiprazole at Week 6. A post hoc analysis suggested a potential confounding of efficacy rating towards symptom improvement in patients who experience known side effects of quetiapine XR.