29th January 2024

Clozapine

Indication

Clozapine is an atypical antipsychotic that is reserved for use in treatment-resistant schizophrenia. It has also been shown to be efficacious against negative schizophrenic symptoms, suicidal and self-harm symptoms. Other indications for clozapine include intolerance to typical or atypical antipsychotics due to extrapyramidal side effects or tardive dyskinesia.

Clozapine drug monitoring

Clozapine is an expensive medication to prescribe, partly due to the fact that it requires intense monitoring via regular blood tests, physical health monitoring and strict regulation on dispensing. The diligent supervision of Clozapine is due to the potentially fatal risk of agranulocytosis. Prior to initiation, the individual must have an FBC to rule out pre-existing haematological disorders (particularly neutropenia). This is then followed by weekly blood tests for 18 weeks, then fortnightly for up to one year. Once stabilised, the frequency of blood tests is reduced to monthly.

Blood test results are reported using a traffic light system.

Green: WBC>3.5, Neutrophils >2.0

Amber: WBC 3.0-3.5, Neutrophils 1.5-2.0

Red: WBC <3.0, Neutrophils <1.5

A green result indicates that the neutrophils are within range, so the patient can continue to take their medication as normal. An amber result should be acted upon with increased blood test monitoring (twice weekly). The clinician (Consultant Psychiatrist) will need to assess the situation and investigate any causative factors that may have contributed to this result, such as concomitant immunosuppressive treatment for another condition, before making a decision regarding a reduction in the treatment dose. If a Red result occurs, then Clozapine will need to be stopped IMMEDIATELY. The patient’s blood counts are low enough to significantly increase their risk of infection and sepsis. Restarting Clozapine following a red result is not straightforward, even if subsequent green results have been obtained. A multidisciplinary team will need to be involved in this decision-making process, weighing up the risks and benefits for each individual patient. It may require re-trialling other antipsychotics before testing it once more.