Predictors of adherence to atypical antipsychotics (risperidone or olanzapine) in older patients with schizophrenia: an open study of 31/2 years duration

Objective: Although the evidence base for the use of antipsychotics in older people with schizophrenia is generally of low quality, it tends to support the use of atypical antipsychotics. Only limited information regarding longer term adherence to these apparently more effective drugs is available. The aim of this study was to determine predictors of adherence to risperidone or olanzapine in patients over 60. Methods: Patients receiving care from old age psychiatrists for their schizophrenia were randomised to treatment with olanzapine or risperidone and were followed for up to 31/2 years. Kaplan Meier curves were generated to assess the univariate effect of randomisation drug on long-term adherence and Cox regression adjusted for baseline variables which may have affected adherence. Results: In total, 60.6% of the 66 patients in the study were still taking their randomised drug by the end of the interval in which they remained under observation (64.7% olanzapine and 56.3% risperidone). This difference was non-significant. No baseline variable was associated with an increased risk of non-adherence, though the delivery form of pre-randomisation drug (oral or depot) was weakly (p = 0.054) associated with patients originally on depot being less likely to be adherent to an atypical drug. Conclusions: Overall adherence with atypical medication was good with almost two-thirds of the patients remaining on their randomisation drug for the interval in which they were under observation. Patients taken off depot were less likely to be adherent but there was no significant difference in adherence between olanzapine and risperidone. Scrutiny of the survival curves suggested that non-adherence is an early event in treatment and patients adherent at 6 months were likely to remain adherent over a longer time period. Copyright (C) 2009 John Wiley & Sons, Ltd.