Objective
Determining whether individual patients differ in response to treatment ('treatment effect heterogeneity') is important as it is a prerequisite to developing personalised treatment approaches. Previous variability meta-analyses of response to antipsychotics in schizophrenia found no evidence for treatment effect heterogeneity. Conversely, individual patient data meta-analyses suggest treatment effect heterogeneity does exist. In the current paper we combine individual patient data with study level data to resolve this apparent contradiction and quantitively characterise antipsychotic treatment effect heterogeneity in schizophrenia.
Method
Individual patient data (IPD) was obtained from the Yale University Open Data Access (YODA) project. Clinical trials were identified in EMBASE, PsycInfo, and PubMed. Treatment effect heterogeneity was estimated from variability ratios derived from study-level data from 66 RCTs of antipsychotics in schizophrenia (N=17,202). This estimation required a correlation coefficient between placebo response and treatment effects to be estimated. We estimated this from both study level estimates of the 66 trials, and individual patient data (N=560).
Results
Both individual patient (r=-0.32, p=0.002) and study level (r=-0.38, p<0.001) analyses yielded a negative correlation between placebo response and treatment effect. Using these estimates we found evidence of clinically significant treatment effect heterogeneity for total symptoms (our most conservative estimate was SD = 13.5 Positive and Negative Syndrome Scale (PANSS) points). Mean treatment effects were 8.6 points which, given the estimated SD, suggests the top quartile of patients experienced beneficial treatment effects of at least 17.7 PANSS points, while the bottom quartile received no benefit as compared to placebo.
Conclusions
We found evidence of clinically meaningful treatment effect heterogeneity for antipsychotic treatment of schizophrenia. This suggests efforts to personalise treatment have potential for success, and demonstrates that variability meta-analyses of RCTs need to account for relationships between placebo response and treatment effects.
Treatment Effect Heterogeneity in Clinical Trials: An Evaluation of 13 Large Clinical Trials Using Individual Patient Data