Antipsychotic dose equivalents and dose-years: a standardized method for comparing exposure to different drugs.
BACKGROUND
A standardized quantitative method for comparing dosages of different drugs is a useful tool for designing clinical trials and for examining the effects of long-term medication side effects such as tardive dyskinesia. Such a method requires establishing dose equivalents. An expert consensus group has published charts of equivalent doses for various antipsychotic medications for first- and second-generation medications. These charts were used in this study.


METHODS
Regression was used to compare each drug in the experts' charts to chlorpromazine and haloperidol and to create formulas for each relationship. The formulas were solved for chlorpromazine 100 mg and haloperidol 2 mg to derive new chlorpromazine and haloperidol equivalents. The formulas were incorporated into our definition of dose-years such that 100 mg/day of chlorpromazine equivalent or 2 mg/day of haloperidol equivalent taken for 1 year is equal to one dose-year.


RESULTS
All comparisons to chlorpromazine and haloperidol were highly linear with R(2) values greater than .9. A power transformation further improved linearity.


CONCLUSIONS
By deriving a unique formula that converts doses to chlorpromazine or haloperidol equivalents, we can compare otherwise dissimilar drugs. These equivalents can be multiplied by the time an individual has been on a given dose to derive a cumulative value measured in dose-years in the form of (chlorpromazine equivalent in mg) x (time on dose measured in years). After each dose has been converted to dose-years, the results can be summed to provide a cumulative quantitative measure of lifetime exposure.
Andreasen
Nancy C
NC
Mental Health-Clinical Research Center, Department of Psychiatry, Carver College of Medicine, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242-1057, USA.
Pressler
Marcus
M
Nopoulos
Peg
P
Miller
Del
D
Ho
Beng-Choon
BC
D014150:Antipsychotic Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use; D002746:Chlorpromazine / Q000493:pharmacokinetics* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006220:Haloperidol / Q000493:pharmacokinetics* / Q000627:therapeutic use; D006801:Humans; D016014:Linear Models; D001523:Mental Disorders / Q000188:drug therapy; D011795:Surveys and Questionnaires; D013810:Therapeutic Equivalency; D013997:Time Factors
D014150:Antipsychotic Agents; D006220:Haloperidol; D002746:Chlorpromazine