Therapeutic monitoring of plasma clozapine and<i>N</i>-desmethylclozapine (norclozapine): practical considerations

SUMMARY Clozapine dose assessment in treatment-refractory schizophrenia is complicated. There a narrow margin between an effective and potentially toxic wide inter-individual variation clozapine metabolic capacity. Moreover, factors such as changes smoking habit, infection/inflammation, co-prescription of certain drugs, notably fluvoxamine, age alter the requirement within individuals. Therapeutic drug monitoring (TDM) plasma N -desmethylclozapine (norclozapine) can help assess adherence, guide dosage guard against toxicity. This article gives overview pharmacokinetics affecting requirements. It then outlines procedures processes TDM, from taking blood sample for laboratory assay or point-of-contact (finger-prick) testing (POCT) to interpreting acting on results.