The hidden magnitude of polypharmacy: using defined daily doses and maximum licensed daily doses to measure antipsychotic load

Background Antipsychotic polypharmacy (“polypharmacy”) is the concurrent prescribing of more than one antipsychotic. It is widely practised, as reported in the literature, and is known to increase the risk of adverse outcomes for patients. Objective To quantify the prevalence and magnitude of polypharmacy in patients with schizophrenia or schizoaffective disorder and identify potential factors contributing to this practice. Setting Armadale Mental Health Service (a public inpatient and outpatient psychiatric facility in Perth, Western Australia). Method A retrospective, cross-sectional study was conducted, evaluating the medical records of adult (18–64 years old) patients fulfilling the established inclusion criteria in the period between August and December 2016. Data collected included the number and doses of antipsychotic(s) prescribed and documented rationale for polypharmacy. Defined daily doses and proportions of maximum licensed daily doses were calculated for all regularly prescribed antipsychotics and were evaluated as measures of antipsychotic load. Main Outcome Measure The percentage prevalence of antipsychotic polypharmacy; defined daily antipsychotic doses and proportions of maximum licensed daily doses. Results Seventy-seven patients were assessed, with a polypharmacy prevalence of 39.0%. Total defined daily doses ranged from 0.9 to 5.9 and maximum licensed daily doses from 0.4 to 2.3. Documented rationales for polypharmacy included poor symptom control, patient’s preference, hesitancy to amend other prescribers’ management plans, off-label antipsychotic indications and medication cross-titration. Conclusion Antipsychotic polypharmacy occurred in more than one-third of patients. Individual antipsychotics were typically prescribed at doses within the licensed range, however, the total proportion of combined maximum licensed doses and combined daily defined doses often exceeded 100%. Due to suboptimal documentation, prescribing rationale was unclear in the majority of cases. The magnitude of polypharmacy aims to foster a greater appreciation of the prescribed antipsychotic load, increasing clinician self-awareness of prescribing practices and facilitating future opportunities to optimise prescribing.