Long-term antipsychotic polypharmacy: how does it start, why does it continue?

Antipsychotic polypharmacy remains a widespread and persistent practice, despite a lack of empirical evidence to support its safety and efficacy. This study aimed to assess antipsychotic treatment prior to the initiation of polypharmacy and ascertained clinicians' reasons for coprescribing long term. We also aimed to determine patterns of antipsychotic coprescription and associated outcome.

Prescription charts across a large mental health trust were reviewed to identify all patients coprescribed two or more antipsychotics excluding clozapine. For those receiving antipsychotic polypharmacy for at least 6 months, electronic patient records were examined to obtain demographic data, documented reasons for initiating polypharmacy and prior prescribing information. Sequence of prescribing, clinical outcome, adverse effects and prescriber considerations to revert to monotherapy were determined.

In all, 38 patients had been receiving two antipsychotics excluding clozapine for longer than 6 months. In 39% of cases patients had been prescribed no or only one antipsychotic before initiation of polypharmacy while 48% had been trialled on clozapine. The most frequently documented reason for coprescribing was that residual psychotic symptoms remained with monotherapy. An improvement in psychotic symptoms was documented in 26% of patients receiving polypharmacy. Prescribers considered stopping polypharmacy in 23 patients.

Antipsychotics were coprescribed largely to improve symptoms and clinical outcome in patients with inadequate response to monotherapy. Polypharmacy was not solely reserved for patients in whom all other therapeutic options had failed. There was some evidence to suggest that patients did benefit from coprescription, albeit at the expense of an increased adverse effect burden. Prospective randomized trials of specific antipsychotic combinations are required to assess the therapeutic utility of this under-researched practice.