Aims and Method: Routine therapeutic drug monitoring in clozapine therapy has previously not been considered justifiable. Using observational data, the clinical utility of annual clozapine assay monitoring is explored within a large mental health trust.
Results: After the introduction of routine monitoring, the rate of clozapine assays rose to 2.3 per patient per year, with a consistent reduction in high-risk clozapine assays (<0.1 mg/L or >1.0 mg/L or any result more than 24 months old). High-risk assays are associated with a mortality rate of 31.6 deaths per 1000 patients, more than twice that of those within the target range (0.35-0.60 mg/L and conducted within the past 12 months) ( P = 0.048).
Clinical Implications: Routine clozapine assay monitoring has significant clinical utility. Our simple but targeted approach can be readily implemented to reduce the number of patients with high-risk clozapine assay levels, potentially reduce all-cause mortality and provide optimal treatment for those with treatment-resistant schizophrenia.