Clozapine levels and outcomes in Serbian patients with treatment-resistant psychotic disorders previously treated without measuring clozapine levels (CLOSER).

Clozapine remains the only pharmacological treatment option for treatment-resistant schizophrenia. Therapeutic drug monitoring (TDM) of clozapine is recommended, although evidence for the therapeutic range of 350-600 ng/ml is limited. In various countries including Serbia, TDM of clozapine is not routinely performed.