Published: 12 December 2013


Update: QT Prolongation with Antidepressants

Prescriber Update 34(4): 44
December 2013

Key Messages

  • QT prolongation appears to be a class effect for all selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), and also occurs with venlafaxine.
  • The potential for QT prolongation to occur should be considered as part of the risk benefit assessment prior to prescribing an antidepressant.
  • There are no high quality data comparing the risk of QT prolongation between different antidepressants (other than citalopram and escitalopram).
  • If QT prolongation or symptomatic arrhythmia occurs during antidepressant treatment, the antidepressant should be stopped or the dose reduced and specialist advice sought.

The data sheets for antidepressants have been updated to include detailed information on the risk of QT prolongation particularly in over-dose. Individual product data sheets should be consulted for advice on the risk associated with a specific antidepressant.

In December 2012, the Medicines Adverse Reactions Committee (MARC) concluded that QT prolongation/Torsades de Pointes is a risk with most of the antidepressants approved for use in New Zealand.

At the MARC's recommendation, a warning has been added to all selective serotonin reuptake inhibitor (SSRI), tricyclic antidepressant (TCA) and venlafaxine data sheets. This warning includes the following information.

  • Cases of QTc prolongation and Torsades de Pointes, have been reported during post-marketing use.
  • The antidepressant should be used with caution in patients with risk factors for QT prolongation.
  • Hypokalaemia and hypomagnesaemia should be corrected prior to treatment.
  • For high risk patients (eg, congenital long QT syndrome or multiple risk factors), ECG monitoring should be performed.
  • Consideration should be given to stopping the antidepressant or reducing the dose if the QT interval is >500ms or increases by >60ms.

QT prolongation is a measure of delayed ventricular repolarisation and is a surrogate marker for the risk of developing the potentially fatal arrhythmia Torsades de Pointes.

The definition of QT prolongation depends on the age and gender of the patient. A QT >500ms or an increase of >60ms during treatment confers a high risk of Torsades de Pointes.

QT prolongation with medicines, including antidepressants, is more likely to occur in the presence of other risk factors. Major risk factors include a genetic predisposition or pre-existing QT prolongation1. Other risk factors include increasing age, female gender, hypokalaemia and hypomagnesaemia, and medicine interactions1.

Further information can be found in the Prescriber Update articles ‘Do All Antidepressants Cause QT Prolongation?’, ‘Citalopram and Escitalopram — Similar Risk of QT Prolongation?’ and ‘Drug-induced QT prolongation and Torsades de Pointes — the facts’13.

Please report any suspected cases of QT prolongation/Torsades de Pointes or arrhythmias with any antidepressant to the Centre for Adverse Reactions Monitoring (CARM).

  1. Medsafe. 2010. Drug-induced QT prolongation and Torsades de Pointes — the facts. Prescriber Update 31(4): 27–29. URL: (accessed 8 November 2013).
  2. Medsafe. 2012. Do all antidepressants cause QT prolongation? Prescriber Update 33(4): 33–35. URL: (accessed 8 November 2013).
  3. Medsafe. 2012. Citalopram and Escitalopram — Similar Risk of QT Prolongation? Prescriber Update 33(1): 3–4. URL: (accessed 8 November 2013).
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