Drugs causing QT prolongation

Drugs associated with QT prolongation include (1,2,3):

• antiarrhythmics:
  • quinidine
  • disopyramide
  • procainamide
  • amiodarone
  • sotalol
• non-sedative antihistamine toxicity
  • terfenadine
  • astemizole
• antimicrobials
  • fluoroquinolones
    • ciprofloxacin and moxifloxacin increase the QTc by less than 10 ms in most cases
    • when used alone and in the absence of other risk factors, fluoroquinolones pose a low risk of clinically significant QT interval prolongation
  • macrolides
    • azithromycin, clarithromycin and erythromycin increase the QTc by less than 5 ms at licensed doses
    • when used alone and in the absence of other risk factors, macrolides pose a minimal risk of clinically significant QT interval prolongation
  • triazole antifungals
    • fluconazole has been associated with QTc more than 500 ms in case reports - occurs mainly in people with non-modifiable patient and medicine risk factors
    • ketoconazole and voriconazole increase QTc by less than 10 ms when used as single agents
• antipsychotics
  • QTc prolongation averages 10 to 20 ms at standard clinical dose
    • for example chlorpromazine, haloperidol, levomepromazine, quetiapine
  • QTc prolongation occurs rarely or only in overdose, with average increases of less than 10 ms at clinical doses
    • for example, aripiprazole, clozapine, prochlorperazine, olanzapine and risperidone
  • QTc interval prolongation is consistently more than 20 ms at normal clinical doses, and carries a higher risk of ventricular arrhythmia
    • includes any intravenous antipsychotic, and any drug or combination of drug used in doses exceeding recommended maximum
• tricyclic antidepressants (TCAs)
  • prolongation of the QTc greater than 10 ms has been reported, with the greatest risk observed with clomipramine
  • monitor ECG, magnesium and potassium in people with non-modifiable risk factors
  • QT interval prolongation with other TCAs, including amitriptyline, imipramine and nortriptyline, appears to occur predominantly in overdose
• methadone
• cocaine has been shown to increase QT intervals acutely (2)
• citalopram or or escitalopram
  • do not prescribe citalopram or escitalopram in people with congenital long QT syndrome, known QT interval prolongation, or who are taking concurrent medicines known to prolong QT interval
  • monitor ECG, magnesium and potassium, before and during treatment with citalopram or escitalopram in people with risk factors
  • monitor for symptoms of QT interval prolongation in people taking citalopram or escitalopram, who are started on CYP2C19 inhibitors, such as omeprazole, esomeprazole, fluconazole, lansoprazole, and cimetidine
  • consider dose reduction of citalopram or escitalopram if symptoms of QT interval prolongation develop or if ECG monitoring demonstrates clinically significant QT interval prolongation
• antiemetics
  • domperidone has been associated with QT interval prolongation and, very rarely, Torsades de Pointes. An increased risk of serious ventricular arrhythmia or sudden cardiac death can occur in:
    • age over 60 years
    • concurrent use with CYP3A4 inhibitors or QT prolonging drugs
    • doses above 30mg daily
    • do not prescribe domperidone in people with bradycardia, congenital QT prolongation, underlying cardiac diseases or receiving other medications known to prolong QT interval or potent CYP3A4 inhibitors
    • monitor ECG, magnesium and potassium before and during treatment in people with non-modifiable patient and medicine risk factors
  • ondansetron
    • do not prescribe ondansetron in people with congenital QT interval prolongation
    • monitor ECG, magnesium and potassium before and during intravenous or prolonged treatment in people with non-modifiable patient and medicine risk factors
    • restrict intravenous ondansetron dose to 16 mg, or 8 mg in patients aged above 75 years
    • intravenous ondansetron doses exceeding 16mg are associated with QTc prolongation of more than 10ms, and an increased risk of ventricular arrhythmias
  • beta-2 agonists
    • no ECG monitoring is required when used alone, at standard inhaled or oral doses, and in the absence of additional patient or medicine risk factors
    • monitor ECG and potassium before and during high-dose, nebulised, prolonged regular treatment in people with non-modifiable patient risk factors or concurrent medicines known to prolong QT interval or lower potassium
    • when used alone and in the absence of other risk factors, beta agonist inhalers pose a low risk of clinically significant QT interval prolongation
  • tamoxifen
    • tamoxifen has the potential to prolong QT interval at standard doses and in overdose
    • monitor ECG, magnesium and potassium, before and during treatment in people with non-modifiable risk factors

Normal QT interval (4):

• 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 (4):

• 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 (5)

For detailed guidance see NHS Specialist Pharmacy Service (August 2026). Commonly used medicines associated with QT interval prolongation

Notes:

• it is beyond the scope of GPnotebook to provide a list of all medicines that prolong the QT interval. The American website http://www.crediblemeds.org/ 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 http://www.evidence.nhs.uk/ ), Summaries of Product Characteristics (SPCs, www.medicines.org.uk) and Stockley’s Drug Interactions (subscription required). Medicines information departments and pharmacists can help with determining the risks of individual medicines

Reference:

1. NHS Specialist Pharmacy Service (August 2026). Commonly used medicines associated with QT interval prolongation
2. CSM/MCA (1996), drug-induced prolongation of the QT interval, Current Problems in Pharmacovigilance, 33, 1-2.
3. RCGP (2007). Drug misuse and dependence: UK guidelines on clinical management
4. NHS Specialist Pharmacy Service (January 2020). What issues should be considered regarding drug-induced QT prolongation?
5. Ayad RF, Assar MD, Simpson L, Garner JB, Schussler JM. Causes and management of drug-induced long QT syndrome. Proc (Bayl Univ Med Cent). 2010 Jul;23(3):250-5.