Antipsychotic Polypharmacy in Schizophrenia Benefits and Risks

Antipsychotic polypharmacy refers to the co-prescription of more than one antipsychotic drug for an individual patient. Surveys of prescribing in psychiatric services internationally have identified the relatively frequent and consistent use of combined antipsychotics, usually for people with established schizophrenia, with a prevalence of up to 50% in some clinical settings. A common reason for prescribing more than one antipsychotic is to gain a greater or more rapid therapeutic response than has been achieved with antipsychotic monotherapy. However, the evidence on the risks and benefits for such a strategy is equivocal, and not generally considered adequate to warrant a recommendation for its use in routine clinical practice in psychiatry. Combined antipsychotics are a major contributor to high-dose prescribing, associated with an increased adverse effect burden, and of limited value in helping to establish the optimum maintenance regimen for a patient. The relatively widespread use of antipsychotic polypharmacy identified in cross-sectional surveys reflects not only the addition of a second antipsychotic to boost therapeutic response, but also the use of as-required antipsychotic medication (mainly to treat disturbed behaviour), gradual cross-titration while switching from one antipsychotic to another, and augmentation of clozapine with a second antipsychotic where the illness has failed to respond adequately to an optimized trial of clozapine. This review addresses the clinical trial data and other evidence for each of these pharmacological approaches. Also reviewed are examples of systematic, practice-based interventions designed to reduce the prevalence of antipsychotic polypharmacy, most of which have met with only modest success. Guidelines generally agree that if combined antipsychotics are prescribed to treat refractory psychotic illness, this should be after other, evidence-based, pharmacological treatments such as clozapine have been exhausted. Further, their prescription for each patient should be in the context of an individual trial, with monitoring of the clinical response and adverse effects, and appropriate physical health monitoring.