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National guidelines to support improved physical health monitoring of patients prescribed clozapine were published by the Scottish Government in 2013.1
It is estimated that up to 60% of patients who are prescribed clozapine experience constipation and although rare, death from complications arising from constipation is estimated at more than three times the rate of death from agranulocytosis.2
Severe complications associated with clozapine induced constipation include intestinal obstruction, faecal impaction and paralytic ileus.
Risk factors for constipation are:
Clozapine can cause reduced gastro-colonic reflexes and possibly reduced intestinal sensitivity to distension; patients may not complain about constipation, therefore they should be asked regularly about bowel habit during clozapine titration/stabilisation and also when on maintenance treatment.
1. During clozapine titration/initiation phase:
2. During clozapine maintenance treatment phase:
Patients with no history of constipation
Patients undergoing treatment for clozapine induced constipation
*Note: for CMHTs, refer to patient’s GP or if symptoms are severe to A&E. For patients in hospital contact the duty doctor. The patient’s Responsible Medical Officer (RMO) must always be informed.
A standardised approach to recording bowel function should be adopted and include numerical values for Bristol Stool Chart type and frequency. For example:
For patients who cannot reliably identify bowel problems, the use of preventative laxative treatment throughout clozapine treatment may be appropriate. It should be noted that prolonged use of stimulant laxatives may lead to degenerative changes in colonic muscles and nerves.
1. National Standard for Monitoring the Physical Health of People Being Treated with Clozapine. Scottish Government. CMO (2013)12
2. Fact Sheet; Constipation. ZTAS December 2013
3. Lactulose versus polyethylene glycol for Chronic Constipation (Review). Cochrane Collaboration (2011)
Last reviewed: 26 May 2020
Next review: 01 May 2023
Author(s): MHS Clozapine Review Group
Approved By: PMG-MH
Reviewer Name(s): Lead Clinical Pharmacist, Clinical Effectiveness Pharmacist