Fatal arrhythmias — drugs and the QT

Published in NPS Direct-AUSTRALIA
Date published: 17 April 2013 About this date

Summary

The potential for some medicines to cause serious cardiac arrhythmias, which could lead to sudden death, has been the subject of recent medicine safety updates from the TGA and the US FDA.

Health professionals need to be aware of which medicines have known QT effects and to consider the risks before prescribing them.

Practice points
Know QT-prolonging medicines
Be aware of which medicines may prolong the QT interval.
Check family history
Before prescribing medicine(s) with known potential for QT effects, take a complete patient history and determine whether there is a family history of long-QT syndrome.
Know risk groups
Groups with a higher risk of fatal arrhythmia due to QT prolongation include:1,2
people with a known history or family history of QT-interval prolongation such as those with torsades de pointes, congenital long-QT syndrome, bradyarrhythmias or uncompensated heart failure
people taking other medicines known to increase the QT interval or affect the metabolism of QT-interval-affecting medicines (Table 1)
people with proarrhythmic conditions such as uncorrected hypokalaemia or hypomagnesaemia
older people and those with cardiac disease, who may be more susceptible to QT-interval prolongation effects.
Check OTC medicines
Be aware that some OTC medicines, such as the antihistamine loratadine, may also have QT-prolongation effects.
Advise patients
Advise the patient of potential adverse effects of the medicine and ensure they know what to do if they experience any signs or symptoms.
When to assess
In high-risk patients assess QT interval before and after starting a medicine with a potential for QT interval effects.
When to avoid medicines with QT effect
In high-risk patients avoiding medicines with known potential for QT effects may be prudent.
Why is the QT interval important?
The QT interval is the time between myocardial contractions, when the ventricular myocardium is repolarising in readiness for the next contraction. QT-interval prolongation is associated with potentially fatal cardiac arrhythmias.3

Drugs and the QT interval
The evidence that some medicines produce QT-interval effects has been accumulating since the 1960s.3,4

Documented cases of sudden death due to arrhythmias resulted in several medicines being removed from the market or their use severely restricted.3,4 As a result, regulatory bodies such as the TGA require the QT effect of any new medicine to be fully assessed before approval.5,6

QT-prolonging medicines — a growing list
Due to the regulatory requirements surrounding QT interval effect investigation, there is now a comprehensive and continually updated list of drugs that have been shown to have the potential to affect the QT interval.1,2,5,6

Table 1 summarises drugs most commonly associated with QT-interval prolongation.

the TGA provides regular updates on safety advice regarding QT-interval prolongation1
other sources of information may be helpful when deciding on medicine choice.

Table 1. Some of the medicines identified as having potential QT-interval effects (recent updates and warnings in bold)1,6
Anti-arrhythmic drugs
amiodarone
sotalol
disopyramide
dofetilide
procainamide
quinidine

Antidepressants
Some SSRIs: citalopram, escitalopram, fluoxetine
moclobemide
Most tricyclic antidepressants
lithium

Antipsychotics
amisulpride
chlorpromazine
haloperidol
ziprasidone
thioridazine

Antihistamines
loratadine
astemizole
diphenhydramine

Antimicrobials
fluoroquinolones: ciprofloxacin, moxifloxacin, sparfloxacin
Macrolides: azithromycin,2 clarithromycin, erythromycin, roxithromycin
Antifungals: fluconazole, voriconazole
Antimalarials: chloroquine mefloquine
Other antimicrobials: pentamidine

Other drugs
cisapride
dolasetron
methadone
arsenic
ondansetron1
domperidone1
fingolimod

G.MOHAN