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Issue 21, December 2012  Produced by NHS Greater Glasgow and Clyde Medicines Information Service DRUG INDUCED QT PROLONGATION
 Prolongation of the QT interval can lead to a What is considered to be a prolonged QT
 Recent warnings have highlighted the risk of The QTc interval is a surrogate marker of proarrhythmic risk and literature differs with regard to the QTc interval that would raise concern over development of arrhythmias. As a guide:  Extra vigilance is required by healthcare professionals to be alert to the risk of drug Borderline QTc interval >440 ms but <500 ms
Although literature differs, a QTc interval within these values is considered borderline prolonged. Consideration should be given to dose reduction of QT prolonging drugs or changing to an alternative non QT prolonging drug. Prolongation of the QT interval can lead to a life threatening ventricular arrhythmia known as torsades de Prolonged QTc Interval >500 ms
pointes which can result in sudden cardiac death. There A QTc interval >500 ms is clinically significant and likely to are a number of widely used drugs which are known to confer an increased risk of arrhythmia. Any drugs which cause QT prolongation. Recently there have been prolong the QT interval should be reviewed immediately. warnings relating to drug-induced QT prolongation for three commonly used drugs – citalopram, domperidone and ondansetron.1,2,3 Extra vigilance is required by Interpretation of the QT interval on an ECG is not
healthcare professionals to be alert to the risk of drug always straightforward and the value noted on the
induced QT prolongation and drug interactions. computerised printout may not always be accurate.
The following website gives some guidance on
There are three mechanisms by which drugs can interact interpretation of the QT interval:
and increase the risk of QT prolongation:
Pharmacodynamic Interaction: The concurrent use of
more than one drug that prolongs the QT interval increases What is considered a significant drug induced
the risk of torsades de pointes and ventricular arrhythmia. change in QTc interval?
Pharmacokinetic Interaction: Some drugs which do
The degree by which a drug changes the QTc interval from not prolong the QT interval themselves can increase the baseline is also important. An increase in baseline QTc of risk of QT prolongation by affecting the metabolism of less than 5 ms is not considered significant and this is the drugs that do. Commonly used examples of this include threshold for regulatory concern. For drugs that increase drugs such as macrolide antibiotics and antifungals which the QTc interval by less than 20 ms the data is inconclusive with regard to arrhythmic risk. A change in baseline QTc of >20 ms should raise concern and a change of >60 ms Effects on Electrolytes: Hypokalaemia and
should raise greater concern regarding the potential for hypomagnesaemia can increase the risk of QT prolongation arrhythmias.8 Experience in long QT syndrome indicates e.g. diuretics can interact with QT prolonging drugs by that for every 10 ms increase in QTc there is a 5% increase in the risk of arrhythmic events.7 Drug induced QT prolongation is often dose related. For example, What is a normal QT interval?
citalopram 20 mg daily has been shown to cause a mean change in baseline QTc of 7.5 ms; this increases to The QT interval varies with heart rate. A number of formulas are used to correct the QT interval for heart rate. A drug induced increase in QTc interval should be assessed Once corrected it is expressed as the QTc interval. The in conjunction with the overall QTc interval. QTc interval is reported on the ECG printout. Normal QTc Interval <440 ms
What are the risk factors for QT prolongation?
In individual cases of torsades de pointes there are often multiple risk factors present. The main risk factors which should be considered are:8,9,10,11
Potentially Modifiable

Electrolyte Disturbances (in particular hypokalaemia, hypomagnesaemia and more rarely hypocalcaemia). Consider the risk of electrolyte disturbance if the patient has GI Concomitant use of more than one drug that prolongs the QT interval Non-modifiable

Cardiac Disease (of multiple origins, including congestive heart failure, ventricular Impaired hepatic/renal function (due to effects on drug metabolism) Thyroid Disease (more common with hypothyroidism and usually normalises with What medications can cause QT prolongation?
It is not possible to include a full list of all medicines known to increase the QT interval in this bulletin. A list of medications known to prolong the QT interval can be found at
bsite categorises drugs based on their risk. It is recommended that you check the lists for drugs commonly used in your area of practice to familiarise yourself Some of the more commonly encountered drugs that are known to prolong the QT interval are Antimicrobials
Antipsychotics (all have some risk)
Protein kinase inhibitors e.g. sunitinib Antiemetics
Table 1: Drugs that can prolong the QT interval.
This list is not exhaustive but is designed to give examples of more commonly used drug What can be done to minimise the risks of drug induced QT prolongation?
The risk of torsades de pointes depends on patient factors and medication history. A safe drug in one patient may be potentially harmful in another. The risks and benefits must be Consider the risk of QT prolongation when starting a new medicine (if unsure of medicine related risk contact pharmacy for advice) Assess patient’s risk factors for QT prolongation Avoid QT prolonging drugs in patients with congenital long QT syndrome Correct any modifiable risk factors such as electrolyte disturbance Where a patient has risk factors and / or is prescribed an interacting
medicine, the first line option is to change to an alternative drug that is not
known to prolong the QT interval whenever possible
When would ECG monitoring be recommended?
It is not practical to recommend an ECG every time a QT prolonging medicine is prescribed, particularly in primary care. The decision should be made on a case by case basis taking into account any additional risk factors the patient has. The following could be considered as a Consider carrying out a baseline ECG prior to starting a QT prolonging drug in patients with risk factors then repeat when the medicine reaches steady state Specialist areas that routinely use QT prolonging drugs may consider developing their own protocols for baseline and follow up ECG monitoring If there is no alternative to using two drugs in combination that are known to prolong the QT interval, especially in patients with additional risk factors, carry out an ECG at baseline and then repeat when the new medicine is likely to reach steady state If long term use of two medicines that can prolong the QT interval is deemed necessary the patient should be followed up and monitored via specialist clinic Any patient on a QT prolonging drug who reports symptoms such as palpitations, lightheadedness and dizziness should be referred for investigation. Additional Comments
If the decision is made to concurrently prescribe two drugs that are known to prolong the QT interval this should be clearly documented in the medical notes. If the combination is contra- indicated specialist advice must be sought. See flowchart and patient scenarios for further information and guidance. References
1. Medicines and Healthcare products Regulatory Agency. Citalopram and escitalopram: QT interval prolongation – new maximum daily dose restrictions (including in elderly patients), contraindications and warnings. Drug Safety Update Dec 2011, Vol 5, issue 5:A1 2. Medicines and Healthcare products Regulatory Agency. Domperidone: smal risk of serious ventricular arrhythmia and sudden cardiac death. Drug Safety Update May 2012, vol 5, issue 3. Medicines and Healthcare products Regulatory Agency. Ondansetron (Zofran): risk of QTc prolongation – important new intravenous dose restriction. Drug Safety Update Aug 2012, vol 6 4. Yap YG, Camm AJ. Drug Induced QT Prolongation and Torsades de Pointes. Heart 5. Al-Khatib SM, Allen LaPointe NM, Kramer JM, Califf RM. What clinicians should know about the 6. Zareba W. Drug induced QT prolongation. Cardiology Journal 2007;14(6):523-533 7. Taylor D, Paton C, Kapur S. The South London and Maudsley NHS Foundation Trust Oxleas NHS Foundation Trust. Prescribing Guidelines in Psychiatry. 11th Edition 2012. Wiley Blackwell Baxter K (ed), Stockley’s Drug Interactions. [online] London: Pharmaceutical Press (accessed April 2012). 9. Roden DM. Drug Therapy: Drug induced prolongation of the QT interval. NEJM 10. Heist EK, Ruskin JN. Drug-induced arrhythmia. Circulation 2010;122:1426-1435 11. Drew BJ, Ackerman MJ, Funk M, Gibler B, Kligfield P, Menon V et al. Prevention of Torsades de Pointes in hospital settings. A scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation 2010;121:1047-1060


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