Clinical Use: Clozaril testing is used to achieve desired plasma levels in patients and testing can be used for monitoring patient compliance and toxicity.
Background: Clozaril (Clozapine), a tricyclic dibenzodiazepine, is used for the symptomatic management of psychotic disorders and is considered an atypical antipsychotic drug. It is currently used primarily for the treatment of patients with schizophrenia or schizoaffective disorders who are at risk for recurrent suicidal behaviour and who have encountered non response or adverse, intolerable extra-pyramidal side effects with more classical antipsychotics.

Seizures, an increased risk of fatal myocarditis, and orthostatic hypotension have also been associated with the use of Clozapine. A side effect of treatment is agranulocytosis, because of the significant risk of agranulocytosis and seizure associated with its use, Clozapine should only be used in patients who have failed to respond adequately to treatment with appropriate courses of standard drug treatments, either because of insufficient effectiveness or the inability to achieve an effective dose because of intolerable adverse reactions from those drugs. Once the desired effect is achieved, the dose may be gradually decreased to keep the patient on the lowest possible effective dose.

Patients being treated with Clozapine should be closely monitored during treatment for adverse reactions. Treatment must include monitoring of white blood cell count and absolute neutrophils count. Clozapine treatment should be discontinued in patients failing to show an acceptable clinical response.

Reference Ranges: ‘Target’ range based on pre-dose samples in adults. A target range of 0.35 – 0.60 mg/L clozapine has been suggested in treatment resistant schizophrenia, although some patients respond at lower concentrations.

There is an increased risk of convulsions at higher doses/ plasma concentrations. Result also incorporates a value for desmethylclozapine (norclozapine) metabolite.

The measurement of norclozapine can be useful in monitoring adherence, and concentrations average 70% those of clozapine during normal therapy.

Associated Diseases:
Patient Preparation: Pre dose sample preferred for interpretation (> 6hrs post-dose).
Specimen Requirements: EDTA plasma
Turnaround Time: 2 working days
Additional Information: CHECK WITH BIOCHEMIST BEFORE SENDING – Usually it is a FBC only that is required. Blood samples for Clozapine measurement are sent directly from the ward and patient is registered.
Referred Test: Referred test
Location: King’s college Hospital