Tottori J. Clin. Res. 7(2), 89-92, 2016

Consistency between defined daily doses and chlorpromazine equivalents
Tsuruhei Sukegawa*
Department of Psychiatry, Tottori Medical Center, National Hospital Organization*Correspondence: sukegawt@tottori-iryo.hosp.go.jp

Abstract
The doses of antipsychotic drugs are increasingly being expressed using the defined daily dose, rather thanthe conventional chlorpromazine equivalent. Previous studies comparing the two units have reported conflicting
results regarding their equivalence. In the present study, the correlation coefficient and coefficient ofdetermination between the logarithms of the defined daily dose and chlorpromazine equivalent were calculated
for 20 antipsychotic drugs available in Japan. Both coefficients were markedly high, at 0.957 and 0.916,
respectively, confirming that there are no essential differences between the two units. Tottori J. Clin. Res. 7(2),89-92, 2016
Key Words: antipsychotic drugs, defined daily dose, chlorpromazine equivalenthighlighted similarities between them. In thecurrent study, the author compared the two units
using their logarithms, to determine potentialsimilarities or differences between them, andconfirmed them to be essentially identical.

1. Introduction
To date, the doses of antipsychotic drugs havefrequently been expressed using the chlorpromazine
equivalent (CPZEq). The CPZEq is defined as thedose of a drug that is equivalent to 100 mg ofchlorpromazine in terms of dopamine D2 receptor
affinity, clinical effects, and other properties1). In
general, a CPZEq of approximately 600 mg isregarded as the optimal dose2,3,4). However,evidence for the use of the CPZEq is unclear, andstandards for the CPZEq vary among researchpapers. Regulations concerning regular reviews of
the CPZEq have yet to be established.
In 1981, the WHO Regional Office for Europe
recommended the ATC/defined daily dose (DDD)
system for international drug utilization studies5).
The DDD refers to the standard daily dose of a drug
for maintenance treatment. It is defined based ondata from a large number of research papers, and isreviewed every 5 years. The DDD values for newdrugs are defined after a 3-year grace period, andsubsequently reviewed every 5 years.
The CPZEq and DDD are expressed in mg.
However, the prescribed daily dose (PDD) can becompared with the DDD through expression as thePDD/DDD.
Rijcken et al.6) emphasized differences
between the DDD and CPZEq, while other studies

2. Methods
Among the 30 types of antipsychotic drugs
available in Japan, the DDD values of 20 wererecorded and clarified based on the ATC-DDD.
Their CPZEq values were calculated using achlorpromazine conversion table reported byInagaki et al.7).
Subsequently, the correlation coefficient andcoefficient of determination between the DDDvalues and the dose equivalent to 100 mg of theCPZEq (100mg CPZEq) values were calculated.
Furthermore, the correlation coefficient andcoefficient of determination between the logarithmsof the DDD values and the logarithms of the 100mg
CPZEq values were calculated.
3. Results
Table 1 shows the DDD and CPZEq of eachdrug. The mean CPZEq value obtained when theDDD values of the 20 drugs were converted intoCPZEq values was 369.3 mg. Table 2 shows thecorrelation coefficient and coefficient of determina1