Plasma Haloperidol Levels: Clinical Response and Fancy Mathematics

To the Editor.—  The article by Smith et al¹ on the relation between plasma haloperidol levels and clinical response suggests a "therapeutic window" relationship with a therapeutic plasma level range between 7.0 and 17.0 ng/mL for hospitalized schizophrenic patients. That is, above 17.0 ng/mL the patient's condition may either fail to improve or even worsen. If this is true (and if it applies to the usual newly [re]admitted schizophrenic patient), our work² and that of Itoh et al³ would indicate that the majority of inpatient schizophrenics in the western world are in the psychotoxic plasma-level range!Itoh and colleagues,³ in a series of 135 schizophrenic patients, and our group,² in a series of 70 patients, found respective correlations of.77 and.82 between dose and haloperidol plasma level. We attribute these high and very comparable correlations to good compliance (we will not enter a patient into the