Indirect comparison analysis of efficacy and safety between olanzapine and aripiprazole for schizophrenia

Aims Indirect comparison (IC) and direct comparison (DC) between aripiprazole and olanzapine for schizophrenia were conducted to compare their efficacy and safety. The objective was to determine the usability of IC and consistency of results delivered by the two comparisons. Factors that might influence the inconsistency of results were also investigated. Methods ICs and DCs were conducted using the change from baseline of the Positive and Negative Syndrome Scale (PANSS) total score as an efficacy endpoint and the dropout rate was selected as a safety endpoint. Placebo and risperidone were used as common comparators for ICs. Results A literature search identified 20 articles. The efficacy analysis gave results on the mean difference in PANSS change (95% CI) of -5.72 (-10.22, -1.22) in ICs using placebo as a common comparator and -7.41 (-15.96, 1.14) in DCs. When using risperidone as a common comparator, it was -9.15 (-20.12, 1.82). In rate ratio analysis of the all cause dropout rate, the IC result was 1.17 (0.83, 1.65) using placebo as a common comparator and 1.56 (0.57, 4.26) using risperidone as a common comparator. Both analyses gave consistent results between ICs and DCs. A slightly lower estimated value was observed in ICs using placebo. Conclusions This study demonstrated that ICs between olanzapine and aripiprazole can deliver results consistent with those of DCs. It is also suggested that the selection of a common comparator is important when control group bias is suspected in the data set.