Using this list
This list provides examples of commonly used medicines associated with QT interval prolongation. It outlines their QT interval prolonging risks and recommended management.
Before using this list, it is important to understand the patient- and medicine-related risk factors for QT interval prolongation. This provides a framework for assessing and managing risk and is essential when interpreting the information in this list and applying it to individual patients.
You can learn more about risk factors for QT interval prolongation in our article:
The list is not exhaustive. Some recommendations may differ from manufacturer guidance based on a medicine’s:
- bioavailability
- degree of QTc prolongation and risk of torsade de pointes (TdP)
- dose
- duration
All clinical decisions must be made on a case-by-case basis, taking into account the patient and medicine risk factors.
Antimicrobials
Fluoroquinolones
Management
No ECG monitoring is required when used alone and in the absence of additional patient or medicine risk factors.
Monitor ECG, magnesium and potassium before and during treatment in people with non modifiable patient and medicine risk factors.
QT interval effects at therapeutic exposure
Ciprofloxacin and moxifloxacin increase the QTc by less than 10 ms in most cases.
Fluoroquinolones affect the QT interval to varying degrees but have very rarely caused torsades de pointes.
Evidence for other fluoroquinolones remains limited.
When used alone and in the absence of other risk factors, fluoroquinolones pose a low risk of clinically significant QT interval prolongation.
Macrolides
Management
No ECG monitoring is required when used alone and in the absence of risk factors.
Do not prescribe in people with a history of QT interval prolongation, ventricular arrhythmia, or significant electrolyte disturbance.
Monitor ECG, magnesium and potassium before and during treatment in people with non-modifiable patient and medicine risk factors. This is particularly important when co-prescribed with medicines known to prolong QT interval that are also CYP3A4 or P-gp substrates.
QT interval effects at therapeutic exposure
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
Management
No ECG monitoring is required when used alone, and in the absence of additional patient or medicine risk factors.
Do not co-prescribe with other QT-prolonging medicines, particularly those that are also CYP3A4 or P-glycoprotein (P-gp) substrates. Triazole antifungals inhibit CYP3A4 and P-gp, which may increase plasma concentrations of co-administered QT-prolonging medicines and increase the risk of QT prolongation.
Short courses, including single doses, may be considered as an exception. Only do so when no alternative treatment is available.
Monitor ECG and electrolytes before and during long course treatment in people with non-modifiable patient and medicine risk factors.
QT interval effects at therapeutic exposure
Fluconazole has been associated with QTc more than 500 ms in case reports. This 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.
Mental Health
Antipsychotics
Many antipsychotics cause ECG changes, and some are causally linked to serious ventricular arrhythmias and sudden cardiac death.
Management
Obtain a baseline ECG before initiating moderate or high QT-effect antipsychotics, particularly:
- chlorpromazine
- haloperidol
- levomepromazine
- quetiapine
Monitor ECG, magnesium and potassium at steady state and following dose increases.
Monitor ECG, calcium, magnesium and potassium regularly in all people with non-modifiable risk factors, or taking concurrent medicines known to prolong QT interval.
Include ECG monitoring as part of annual physical health reviews in all individuals receiving long term antipsychotic treatment.
QTc interval effects at therapeutic exposure
The Maudsley Prescribing Guidelines categorises antipsychotic medicines according to their risk of QTc prolongation into four categories below.
No effect
QTc prolongation has not been reported at therapeutic doses or in overdose.
For example, brexipiprazole and lurasidone.
Low effect
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.
Moderate effect
QTc prolongation averages 10 to 20 ms at standard clinical doses.
For example, chlorpromazine, haloperidol, levomepromazine, and quetiapine.
High effect
QTc interval prolongation is consistently more than 20 ms at normal clinical doses, and carries a higher risk of ventricular arrhythmia.
This includes any intravenous antipsychotic, and any drug or combination of drug used in doses exceeding recommended maximum.
Selective Serotonin Reuptake Inhibitors (SSRIs)
Management
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.
QT interval effects at therapeutic exposure
QTc changes are not usually seen with most SSRIs, at normal clinical doses.
Fluoxetine, paroxetine and sertraline have no effect on QTc at licensed doses
Citalopram and escitalopram increase the QT interval in a dose-dependent manner, with mean QTc increases of less than 10 ms at licensed doses.
Tricyclic antidepressants (TCAs)
Management
Monitor ECG, magnesium and potassium in people with non-modifiable risk factors.
QT interval effects at therapeutic exposure
TCAs can prolong the QT interval through sodium and potassium channel blockade.
Prolongation of the QTc greater than 10 ms has been reported, with the greatest risk observed with clomipramine.
QT interval prolongation with other TCAs, including amitriptyline, imipramine and nortriptyline, appears to occur predominantly in overdose.
Antiemetics
Dopamine receptor antagonists
Management
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.
QTc interval effects at therapeutic exposure
Domperidone has been associated with QT interval prolongation and, very rarely, TdP. 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
Haloperidol’s QTc prolonging effect at typical antiemetic doses is expected to be lower than at antipsychotic doses.
Metoclopramide has been associated with QT prolongation, reported predominantly with intravenous administration.
Prochlorperazine has a low risk and is rarely associated with QT prolongation.
5HT3-receptor antagonists
Management
Do not prescribe ondansetron in people with congenital QT interval prolongation.
No monitoring is required in the absence of risk factors or in oral use.
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.
QT interval effects at therapeutic exposure
Ondansetron and palonosetron pose a low risk of QT interval prolongation in the absence of patient risk factors.
Intravenous ondansetron doses exceeding 16mg are associated with QTc prolongation of more than 10ms, and an increased risk of ventricular arrhythmias, including TdP.
Respiratory
Beta-2 agonists
Management
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.
QT interval effects at therapeutic exposure
All beta-2 agonists can cause dose-dependent hypokalaemia and tachycardia, via beta-2 mediated intracellular potassium shift.
The magnitude and clinical significance vary by route. The risk is generally greatest with intravenous administration, followed by nebulised, then standard inhaled, and least with oral.
At standard inhaler doses, serum potassium reductions are usually mild and transient, and rarely result in clinically significant QT interval prolongation.
When used alone and in the absence of other risk factors, beta agonist inhalers pose a low risk of clinically significant QT interval prolongation.
The likelihood of a clinically significant interaction with other medicines known to prolong QT interval is considered low.
Endocrine and oncology
Tamoxifen
Management
Monitor ECG, magnesium and potassium, before and during treatment in people with non-modifiable risk factors.
QT interval effects at therapeutic exposure
Tamoxifen has the potential to prolong QT interval at standard doses and in overdose.
There is no well-established QTc prolongation value for tamoxifen alone, although the risk of TdP is considered low.