What does QT prolongation mean?

It means a medicine lengthens the time the heart takes to recharge between beats. Usually harmless alone, but a longer QT can raise the risk of a dangerous rhythm, especially when several QT medicines combine.

Which medicines cause QT prolongation?

Certain antibiotics, antifungals, antidepressants, antipsychotics, anti-nausea, and heart-rhythm medicines. The risk adds up when several are combined or potassium/magnesium is low — ask your pharmacist.

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QT prolongation: medicines and heart rhythm

By the RxSafeCheck team · Educational, reviewed for plain-language clarity · Morning Mind LLC

You may see a warning that a medicine can "prolong the QT interval." Here's what that means in plain language and why combinations matter.

What QT prolongation is

The QT interval is the time the heart takes to recharge between beats. Some medicines lengthen it slightly. On its own that's often harmless, but a longer QT can, in some people, raise the risk of a dangerous fast rhythm.

Why combinations matter

The effect adds up when you take more than one QT-affecting medicine, or when levels are high. Types that can affect QT include certain antibiotics, antifungals, antidepressants, antipsychotics, anti-nausea, and heart-rhythm medicines.

What raises the risk

Taking two or more QT-affecting medicines.
Low potassium or magnesium.
Existing heart rhythm problems or a family history.

What to ask: If you're on more than one QT-affecting medicine, ask your pharmacist or prescriber whether you need an ECG or a potassium/magnesium check, and whether any medicine has an alternative.

RxSafeCheck flags when two or more QT-affecting medicines appear together, grouped under heart rhythm.

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Important: This article is educational and not medical advice. It does not replace your pharmacist or prescriber. Always confirm decisions about your medicines with a qualified professional, and call your local emergency number for emergencies. In the U.S., Poison Control is 1-800-222-1222.