Background: The defined daily dose (DDD) from the Anatomical Therapeutic Chemical Classification System can be utilised as a reference for international drug utilization research, according to the World Health Organization. Alternatively, chlorpromazine equivalent (CPZeq) is a traditional method that has been used to indicate the dose of antipsychotics for decades. The aim of this study was to investigate and compare the DDD and CPZeq methods in order to calculate the total antipsychotic dose of inpatients with schizophrenia.

Methods and Findings: Six countries (China, Hong Kong, Japan, Korea, Singapore, and Taiwan) participated in antipsychotic prescription pattern surveys conducted four times during 2001, 2004, 2009, and 2016. The antipsychotic loading (APL) values of each prescription, calculated using the DDD and CPZeq methods, and their correlations were compared. A total of 6986 prescriptions from inpatients with schizophrenia were analysed. Spearman’s correlation coefficients (CCs) between the DDD and CPZeq were 0.853 overall, and 0.884, 0.843, 0.850, and 0.786 for the individual surveys (1–4, respectively). The CC of FGA only (n= 2442), SGA only (n= 2992) and combination of FGA and SGA (n= 1552) were 0.901, 0.757, and 0.883, respectively. The mean APL values calculated by the DDD and CPZeq methods were 1.73±1.40 and 597.0±530.7 mg, respectively.

Conclusions: Significant correlations between the DDD and CPZeq methods were observed. The decreasing trend in CC values from the first to the fourth survey might be attributed to the more common use of second-generation antipsychotics in recent years. We suggest that