Plasma clozapine concentrations as a predictor of clinical response: a follow-up study.

We investigated the relationship between plasma clozapine concentrations and clinical response in treatment-refractory schizophrenic patients. In a previous study, we found that plasma drug concentrations above 350 ng/mL maximized clinical response in a group of 29 patients. This study represents a follow-up of these original 29 patients over approximately 2 1/2 years of clozapine treatment.