Published: June 2005
Publications
Thioridazine Prescribing Reminder
Prescriber Update 26(1): 9
June 2005
Medsafe Pharmacovigilance Team
Prescribers are reminded that thioridazine is a third-line antipsychotic agent and should only be prescribed in patients for whom the therapeutic benefits clearly outweigh the risk of arrhythmia from QT-prolongation.
Thioridazine (Aldazine®, Melleril®*) increases the risk of arrhythmia from QT-prolongation. Consequently, the Medicines Adverse Reactions Committee (MARC) recommended changes to how thioridazine is prescribed in New Zealand. The following advice was issued in June 2001 (see www.medsafe.govt.nz/profs/PUarticles/thioridazine.htm), which the MARC would like to reiterate.
Thioridazine is contraindicated in the following circumstances, all of which are risk factors for arrhythmia:
- use with medicines which inhibit the metabolism of thioridazine (cimetidine, most antidepressants, pindolol, propranolol)
- use with medicines which prolong the QT-interval (some antiarrhythmics, most antipsychotics, cisapride)
- use in patients with predisposing factors for arrhythmia or pre-existing QT-prolongation (QTc ≥ 500ms).
Thioridazine should be initiated only by a specialist and only as third-line therapy. In addition, the following precautions should be observed for new patients:
- assess for risk factors for arrhythmia
- check the QTc-interval and serum potassium
- use the minimum effective dose
- observe a maximum of 200mg daily ordinarily
- use dosages above 200mg daily up to a maximum of 600mg daily only under specialist supervision and only with QTc-interval monitoring following each increase.
For all patients currently taking thioridazine:
- assess for risk factors for arrhythmia
- check the QTc-interval and serum potassium
- doses above 200mg daily require review by a specialist
- reduce the dose if QTc-interval ≥ 500ms
- withdraw thioridazine if QTc-interval is persistently ≥ 500ms, or in the presence of any contraindication.
Any children taking thioridazine should also have their therapy reviewed by a specialist. If thioridazine discontinuation is necessary, gradually reduce the dose over a period of one month and concurrently introduce alternative medication. Specialist supervision may be advisable for the withdrawal process.
* Novartis has advised that from 1 July 2005 supplies of Melleril will no longer be available.
Competing interests (authors): none declared.