Precautions/warnings concerning use of thioridazine

• all patients who are to be treated with thioridazine should have baseline electrolytes measured and ECG screening; these should be repeated after each dose increase and at 6-monthly intervals; treatment should be commenced at the lowest possible dose and slowly titrated
  
  
• patients should be checked for potentially interacting drugs or other risk factors for cardiac disease
  
  
• thioridazine is metabolised by cytochrome P450 2D6. Therefore drugs which inhibit this enzyme or are metabolised by it have the potential to increase thioridazine plasma levels and thus cardiotoxicity
  
  
• additive cardiotoxic effects may occur if other drugs which prolong the QTc interval are taken concurrently with thioridazine
  
  
• contraindications to thioridazine use include clinically significant cardiac disorders (including dysrhythmias), conduction disorders or a history of QTc prolongation
  
  
• drugs or medical conditions which can lead to electrolyte imbalance also predispose to thioridazine induced ventricular arrhythmias (1)
  
  
• treatment with thioridazine should be supervised by a consultant psychiatrist

The summary of product characteristics should be consulted before prescribing this drug.

Reference:

• 1) Message from Professor Alasdair Breckenridge, Chairman, Committee on Safety of Medicines, Thioridazine: restricted indications and new warnings on cardiotoxicity, 11/12/00.