Serum level of clozapine and relapse

The case of a young female patient is reported who was diagnosed as having her first manifestation of a paranoid schizophrenic psychosis and who was treated, mainly with clozapine, at the university psychiatric clinic for 3 years, i.e. subsequent episodes are included. Serum levels of clozapine were measured 29 times. Thus, a rather narrow-meshed schedule of therapeutic drug monitoring (TDM) of clozapine was applied. It was found that relapses occurred repeatedly at low serum levels of 48, 109, and 138 ng/mL because of noncompliance by the patient during outpatient treatment, and also because the dose was lowered too hastily after partial response during inpatient treatment. Intoxication was evident at a high serum level of clozapine of 1158 ng/mL during a trial with a dose of 800 mg/d, although moderate serum levels had been found at the same dose some months before. It is concluded that TDM should be considered as being an adjunct to the treatment of schizophrenic and schizoaffective patients with clozapine, not only during inpatient treatment, but also during maintenance outpatient treatment.