Managing Clozapine Patients in Acute Hospitals

Introduction

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. 

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:

  • The patient or their carer
  • Patient's own supply
  • Woodland View Pharmacy Department
  • Psychiatric letters on Clinical Portal
  • Patient's Community Pharmacy

Once clozapine treatment has been identified, the dose can be confirmed. Ideally the patient's own supply should be used; however, a supply can be obtained by contacting the ward clinical pharmacist or, if not available, the pharmacy department. If out of hours, the on-call pharmacist for the hospital should be contacted. 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.
  • Clozapine Blood Validity.
    • Clozapine can cause neutropenia and potentially fatal agranulocytosis. Regular monitoring of Full Blood Count (FBC) with differential white cell and neutrophil count is mandatory. All patients prescribed clozapine are registered with the monitoring service provided by the manufacturer of the brand of clozapine they are prescribed.
    • It is important to ensure on admission that the patient has a valid green or amber blood result. This is based on white cell and neutrophil count predominantly, and is decided on by the relevant clozapine patient monitoring service provided by the manufacturer. This should be confirmed with the Woodland View Pharmacy Department. If this is out with normal working hours, if open, the patient’s community pharmacy can be contacted to confirm this. If the community pharmacy is not available and a dose is required that night then the on-call pharmacist for the hospital should be contacted who can liaise with the Woodland View Pharmacy team to confirm blood validity. If the next dose is required in the morning then staff should check with Woodland View Pharmacy Department that morning before administering clozapine. N.B. The blood validity is based on specific blood parameters and is not related to clozapine plasma levels. 
  • Compliance. Patients often take a dose that differs from that prescribed for them – usually this is a lower dose. Initially prescribe what they actually take until advice has been sought from Mental Health*. Do not prescribe a higher dose than what they are prescribed. 
  • 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 NHSAAA’s Guideline on Drug-Induced QT Prolongation.
  • 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 Woodland View.
  • 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.
  • Constipation. It is very important to manage constipation promptly to avoid clozapine-related toxicity and potential bowel obstruction.
  • Smoking status. If the patient’s smoking status will change significantly during the duration of their in-patient stay this should be discussed with Mental Health*. Changes to smoking status will impact clozapine plasma levels.

*Seek advice from Psychiatric Liaison Services, Woodland View Pharmacy Department or, when these services are unavailable, the on-call pharmacist.

Discharge planning

  • Ward staff should liaise with the ward clinical pharmacist or, if not available, the pharmacy department to determine how many days of clozapine should be supplied on discharge. The pharmacy team should then liaise with Woodland View Pharmacy Department.

Contacts

 

Guideline reviewed May 2025
Page updated August 2025

 




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