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Drugs causing QT prolongation

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Drugs associated with QT prolongation include (1):

  • tricyclic antidepressants
  • antiarrhythmics:
    • quinidine
    • disopyramide
    • procainamide
    • amiodarone
    • sotalol
  • non-sedative antihistamine toxicity
    • terfenadine
    • astemizole
  • antimalarials
    • especially halofantrine
  • antipsychotics
    • notably droperidol and thioridazine
  • cisapride

  • methadone

  • cocaine has been shown to increase QT intervals acutely (2)

  • citalopram (3)

  • ondansetron (3)

Normal QT interval (3):

  • QT interval varies with heart rate
  • females have a longer QT interval than males
  • definitions vary in the literature but as a guide, normal QTc intervals are <450 milliseconds (ms) for men and <460 ms for women
  • a QTc between these values and 500 ms is considered prolonged
    • a QTc >500 ms is considered clinically significant and is likely to confer an increased risk of arrhythmia

Magnitude of drug induced changes in QT interval (3):

  • the degree by which a drug changes the QTc interval from baseline is also important
    • an increase in baseline QTc of around 5 ms or less is not considered significant and this is the threshold for regulatory concern
    • for drugs that increase the QTc interval by less than 20 ms the data are inconclusive with regard to arrhythmic risk
      • a change in baseline QTc of >20 ms should raise concern and a change of >60 ms should raise greater concern regarding the potential for arrhythmias
      • evidence from congenital long QT syndrome indicates that for every 10 ms increase in QTc there is a 5-7% increase in risk of torsades de pointes
    • drug-induced QT prolongation is often dose related and risk of torsades de pointes is increased with intravenous administration (particularly if given rapidly)
    • mechanism for most potential QT-prolonging medications is inhibition of the KCNH2-encoded HERG (human ether-a-go-go related gene) potassium channel (4)


  • it is beyond the scope of GPnotebook to provide a list of all medicines that prolong the QT interval. The American website has regularly updated lists of medicines which cause prolongation of the QT interval. Information can also be found in the British National Formulary (BNF, available via ), Summaries of Product Characteristics (SPCs, and Stockley’s Drug Interactions (subscription required). Medicines information departments and pharmacists can help with determining the risks of individual medicines


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