The aim of our study was to assess the antipsychotic polypharmacy (APP) prevalence in a psychiatric hospital and to find the supporting evidence for the 10 most prescribed two-drug combinations. Secondarily, how many included clozapine, prevalence in the elderly, high dosage and clinically relevant interactions were also assessed.

Clinicodemographic and computerized prescription data on 29th March 2011 were collected. High dosage was defined as more than 1000 mg of chlorpromazine equivalents (CPZeqs). A t test for unpaired measures was applied to compare means of dosage (CPZeq) and age among patients on APP vs. monotherapy. The χ² test was applied to compare proportions of patients on a high dose on APP vs. monotherapy. GraphPad Prism 5 software was used to perform statistical analysis.

From 201 patients admitted on 29th March, 172 had any antipsychotic prescription. APP prevalence was 47.1%, corresponding almost to 24% of elderly patients. Quetiapine was the drug most prescribed in combination, achieving a prevalence rate of 56.8%. Clozapine was not included in 67% of all combinations. Supporting evidence for two-drug combinations was only found for 6 of the 10 most prescribed. Relevant interactions were found in 12 patients on APP. The mean CPZeq dose and percentage of patients on high dosage were significantly higher in the APP than in the monotherapy group (1162±776.1 mg vs. 455.4±369.3 mg; 54% vs. 9%, respectively; P<.0001).

Our study shows that APP was being considered earlier in the management plan than what guidelines recommend. This practice was associated with higher total antipsychotic doses. Until further clinical trials are available, a wise APP practice will require a thoughtful choice of products guided by patient's prior history and interaction liability, a proper consent by the patients or their representatives and a careful monitoring of clinical outcomes and emerging side effects in order to avoid indefinite administration of ineffective and potentially harmful combinations.