Vaquero-Baez M, Díaz-Ruíz A, Tristán-López L, et al. - In the present study, researchers examined the value of measuring plasma clozapine (CLZ) and N-desmethyl clozapine (DMC) as biomarkers to relate drug concentrations with the appearance of preclinical adverse hematic effects. They validated a high-performance liquid chromatographic method, employing a diode-array (ultraviolet) detector, to ascertain reliable concentrations of CLZ and DMC, its main metabolite, in plasma of 41 schizophrenic patients taking CLZ. They identified the analytical method as linear, reproducible, and stable to estimate concentrations of CLZ between 30 and 1000 ng/mL, while 12.5–560 ng/mL of the metabolite. Findings suggest an independent correlation of plasma levels of CLZ and time taking the drug with blood neutrophils and leucocytes, hence they suggest monitoring of plasma CLZ as valuable in the clinical practice to ascertain safe dosing of the drug.