Dropout rates in randomised antipsychotic drug trials

It has been assumed that new atypical drugs improve treatment compliance due to fewer adverse effects. Data supporting this assumption are scarce.

The aim of this study was to study attrition rates in randomised controlled trials of oral administration of conventional antipsychotic drugs, atypical antipsychotic drugs and placebo.

The database of the Schizophrenia Module of the Cochrane Library was utilised for the present study. The data in the Cochrane Module are collected by identifying relevant randomised controlled trials from several electronic databases and other sources. Number of dropouts was defined as patients leaving the study preterm due to any reason.

Data from 328 treatment groups, consisting of 18,585 randomised subjects from 163 drug trials, were entered in the analysis. One-third of the subjects had dropped out of the trials. The dropout rates significantly increased for each calendar year. Year of trial publication, type of drug and trial length remained statistically significant contributors to dropout rates. In a model incorporating year of publication and trial length, placebo groups and groups treated with conventional antipsychotics had significantly higher attrition rates than groups treated with atypical drugs. When clozapine-treated groups were excluded from the analysis, no statistically significant advantage for atypical drugs over conventional drugs remained.

Trial data implicate that a better compliance can be achieved by favouring atypical drugs rather than conventional alternatives in the treatment of schizophrenia. However, this effect is found only when groups treated with the atypical antipsychotic clozapine are included in the analysis. Our study did not find evidence for a statistically significant superiority in acceptability of novel atypical drugs when compared to conventional antipsychotics.