Adjunctive use of atypical antipsychotics and anticholinergic drugs among patients with schizophrenia

Treatment of schizophrenia with antipsychotics is often associated with extrapyramidal symptoms (EPS), a disorder involving involuntary muscle movement. Because EPS are often associated with the use of antipsychotics, anticholinergic agents are often indicated.

In this observational, retrospective study, we examined whether the initiation of olanzapine or risperidone, the two most widely prescribed atypical antipsychotics, is related to the adjunctive use of anticholinergic agents.

We identified patients with schizophrenia from outpatient clinics in the Veterans Health Administration (VA) and defined initiation of olanzapine or risperidone as patients who were not on any antipsychotics for 6 months and subsequently initiated on the target drug between 1/4/1999 and 31/3/2000. The data were analysed using tests of means or chi-square tests.

The study yielded two major findings. First, compared with risperidone initiators, there were significantly fewer olanzapine initiators who used at least one anticholinergic agent adjunctively. Secondly, among olanzapine or risperidone initiators, patients who used at least one anticholinergic agent adjunctively tended to stay on the target drug significantly longer than those who did not use any anticholinergic agent adjunctively with the target drug.

As the use of anticholinergics is a proxy for the presence of EPS, these findings suggest that risperidone may be more associated with EPS than olanzapine. However, to assess the benefits and side effects associated with olanzapine or risperidone, future research needs to examine various patient outcomes resulting from the initiation of each drug.