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Dr. Alessandro Giardini
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If your child has long QT syndrome, a trip to the pharmacy can suddenly feel like a minefield. The good news is that most everyday medicines are perfectly fine.
Long QT syndrome affects the heart's electrical recovery between beats. Certain medicines can lengthen that recovery time further, called QT prolongation, and in susceptible people this can occasionally trigger a dangerous heart rhythm. That's the mechanism behind all the caution, and it's worth understanding because it explains why some medicines matter and most simply don't.
Paracetamol and ibuprofen, the two most commonly used medicines for pain and fever in children, are not QT-prolonging and can be used normally. Most antihistamines used for hay fever and allergies, including cetirizine and loratadine, are also considered safe. Standard childhood vaccines carry no QT-related concern.
A specific group of antibiotics, the macrolides, which includes erythromycin, clarithromycin and azithromycin, are known to prolong the QT interval and should be avoided where a suitable alternative exists. Ondansetron, commonly given for nausea and vomiting, is another one to flag to any prescriber, along with domperidone, sometimes used for the same purpose. Certain older antihistamines and some medicines used for psychiatric or neurological conditions also carry QT-prolonging effects, though these are less commonly relevant in day-to-day paediatric care.
The most useful habit for any family managing Long QT syndrome is simple: tell every doctor, dentist, pharmacist and out-of-hours service that your child has this diagnosis before any new medicine is prescribed, even for something that seems unrelated, like a dental procedure or a minor infection. Most prescribers will check straightaway once they know, and reputable, regularly updated lists of QT-prolonging drugs exist for exactly this purpose, so nobody has to rely on memory alone. The one I recommend is www.crediblemeds.org. Parents can register so they can access up to date lists and receive regular updates once new medications are added to the list or when medications are removed from the list because of new medical evidence.
It's also worth keeping a simple written note, on your phone or in a bag you take everywhere, listing your child's diagnosis and any medicines already known to be avoided. In an urgent situation, this single piece of information can save valuable time.
If you're ever unsure whether a specific medicine is safe for your child, it's always worth checking directly rather than guessing either way. Dr Giardini and his team can advise quickly on individual medicines as they come up, and a clear management plan can be put together so day-to-day decisions like this feel far less daunting.
Yes. Paracetamol is not known to prolong the QT interval and can be used as normal for pain or fever in a child with long QT syndrome.
Macrolide antibiotics, including erythromycin, clarithromycin and azithromycin, are known to prolong the QT interval and are generally avoided in favour of alternatives where possible.
Yes. Routine vaccines carry no known QT-related risk and can be given according to the normal schedule.
Tell the prescribing doctor, dentist or pharmacist about the long QT diagnosis before the medicine is given, and check against an up to date list of QT-prolonging drugs. If there's any doubt, it's worth confirming directly with your child's cardiology team.
Ondansetron is known to prolong the QT interval and is generally best avoided or used with specific caution in children with Long QT syndrome, so it's worth flagging this to whoever is treating your child for nausea or vomiting.
Author: Dr. Alessandro Giardini, MD, PhD, Consultant Paediatric Cardiologist
Written 18/08/2026
Last reviewed 18/08/2026