OBJECTIVE: The purpose of this study was to determine if plasma
clozapine levels were associated with treatment response. METHOD: To
examine this question, neuroleptic nonresponsive patients with
schizophrenia or schizoaffective disorder were given clozapine, which was
titrated to 500 mg/day by day 14 of treatment, and the dose was held fixed
at least through day 21. Subsequently, clozapine doses were adjusted as
clinically indicated, up to a maximum of 900 mg/day. Plasma clozapine
levels were obtained at weeks 3 and 6, and standard clinical ratings (Brief
Psychiatric Rating Scale [BPRS] and Clinical Global Impression) were done
at baseline and at weeks 3 and 6. RESULTS: Data from 45 subjects were
analyzed. There were no correlations between plasma clozapine levels and
change in BPRS scores at treatment weeks 3 and 6. However, when the
subjects were classified as responders or nonresponders, therapeutic
response was associated with clozapine blood levels above 350 ng/ml.
CONCLUSIONS: This study suggest that clozapine blood levels are correlated
with clinical response.