Managing Clozapine Patients in Acute Hospitals


The appropriate use of clozapine in acute care is important as missed doses may result in relapse of psychotic illness and if more than 48 hours has elapsed since the last dose, necessitate re-titration. Clozapine may not always appear on the Emergency Care Summary (ECS). It should be noted that acute hospital sites do not routinely stock clozapine; it is prescribed and dispensed within the specialist mental health services. The following guidance supports the safe and effective management of patients prescribed clozapine admitted to acute hospitals. More detailed advice, including the management of clozapine induced constipation, can be found in a series of Medicines Update blogs available at

Medicines Reconciliation/Supply

If the patient has a past diagnosis of schizophrenia or psychosis in Parkinson's disease but there is no antipsychotic listed in the ECS, it is essential to check if the patient is receiving clozapine. Use other sources to ensure accurate medicines reconciliation. These include:

  • A clozapine alert within the GGC Mental Health Summary in Clinical Portal. Note: the Mental Health Summary contains a warning about accessing highly sensitive information, the need to confirm clozapine treatment is an appropriate reason to access the Mental Health Summary.
  • The patient or their carer.
  • Patient's own supply.
  • The patient's Community Mental Health Team.

Once clozapine treatment has been identified, the dose can be confirmed and a supply obtained by contacting Leverndale Pharmacy (see Appendix 6 for contact details) or the out of hours Mental Health Pharmacy on call team (access via switchboard). Alternatively, the patient's own supply can be used. Ensure the supply is transferred with the patient between wards /hospitals to avoid a break in clozapine treatment.

Points to consider before prescribing clozapine

  • Reason for admission. Consider if the patient's presentation may be related to clozapine (e.g. neutropenia, aspiration pneumonia, cardiac symptoms, seizures, increased temperature). Clozapine induced constipation is very common and may lead to fatal bowel obstruction if ignored. Seek prompt advice from Mental Health* before prescribing clozapine.
  • Last clozapine dose. If it is more than 48 hours since the patient last took a dose, treatment should be re-titrated on advice from Mental Health* starting from 12.5mg. Serious adverse effects including tachycardia, postural hypotension, myocarditis and seizures can occur if a full treatment dose is administered after a break in treatment.
  • Compliance. Patients often take a dose that differs from that prescribed for them. Initially prescribe what they actually take until advice has been sought from Mental Health*.
  • Interaction. Always check for interactions that can increase the incidence of clozapine related side effects e.g. smoking status, drugs known to cause neutropenia or QT prolongation. See BNF for details as well as the clozapine blog articles and the Medicines Update Extra (MUE 08) Drug Induced QT Prolongation article at  
  • Clozapine plasma levels. A number of factors may affect clozapine plasma levels resulting in the increased risk of dose related side effects e.g. change in smoking status, acute infection including COVID 19, inflammatory processes, interacting medicines and constipation. Seek advice from Mental Health Pharmacy Services or Liaison Psychiatry as necessary. Clozapine plasma levels are not processed by local labs but kits for undertaking clozapine plasma levels may be obtained from the pharmacy at Leverndale Hospital (see Appendix 6 for contact details).
  • Surgery. If possible avoid clozapine for 12 hours prior to general anaesthesia. The next due dose may have to be postponed following surgery if there are issues with low blood pressure or excessive sedation. Clozapine should be restarted within 48 hours at normal dose. If it is more than 48 hours since last dose, treatment should be re-titrated on advice from Mental Health*, starting from 12.5mg.

* Always seek advice from Leverndale Pharmacy (see Appendix 6 for contact details), Psychiatric Liaison Services or the Mental Health Pharmacy on call service (access via switchboard) with regard to the management of clozapine patients. Further guidance about the use of clozapine can be found on the MyPsych website or mobile device app which can be downloaded from the Apple or Google Play Stores free of charge. For more information please contact


Guideline reviewed: May 2023

Page last updated: October 2023