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For Healthcare Providers: Frequently Asked Questions about drug-induced QT prolongation and torsades de pointes (TdP).

How prevalent is drug- induced LQTS (long QT syndrome) in the general population?

The incidence or prevalence of drug-induced LQT in the general medical population has not been determined. Many people might experience a prolonged QT when taking a medication, but unless they have an ECG recorded, it wouldn't be detected. A drop in serum potassium or another change in health that might affect cardiac repolarization could change a well-tolerated medicine to one that is life threatening for a person.

Do the drugs on the lists have the same effects on all patients?

No, many people take medications that may prolong QT slightly without causing any problem but unfortunately others receiving the same drug and dose, develop lethal arrhythmias. There is evidence that some of those who develop serious arrhythmias, like TdP, have predisposing genetic factors.

Are there patients without congenital LQTS who are particularly vulnerable to QT prolongation and torsades de pointes?

Some people with a normal QT interval have extreme sensitivity to drugs that can prolong the QT. They may be silent carriers of genetic mutations for Long QT syndrome. Women tend to have a greater QT prolongation in response to these drugs (see comments on our lists).

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It is important to remember that the patient's cardiac, kidney and liver function, as well as electrolyte profile, can increase vulnerability to QT prolongation and torsades de pointes, even in the absence of congenital LQTS. Genetic predisposing factors and diagnostic tests are available but they only aid in making the diagnosis in some patients.

Are there specific guidelines for monitoring the QTc for persons who are taking QT-prolonging drugs?

We recommend that you:

  1. If possible, do not prescribe QT-prolonging drugs to anyone with a QT>440ms (female) or 420ms (male).
  2. Do not allow the QT to exceed 500ms during titration with these drugs.
  3. Be aware of drug interactions that could result in greater exposure to the QT- prolonging drugs by blocking their metabolism or delaying clearance.

Does female gender increase the sensitivity to QT-prolonging drugs and raise the risk of TdP with some drugs?

Yes it does. Even at equivalent blood levels of the drugs, females have an increased sensitivity to many of the drugs that prolong the QT interval and they have a higher incidence of TdP. Look for comments regarding female gender for specific drugs on our lists.

Is there an increased risk of developing TdP due to interactions between prescription drugs and OTC drugs or supplements? What about foods? 

Yes, in some cases. Interactions are highly variable in their expression and sometimes difficult to predict. The antacid drug famotidine is known to cause QT prolongation and is available in most countries without a prescription.  Some dietary supplements that contain ephedrine have been found to prolong the QT interval and would be especially dangerous if combined with prescription drugs that have this action. Some foods can cause an interaction with drugs; for example, grapefruit juice inhibits the enzyme cytochrome P450 3A4, which metabolizes many of the medications known to prolong the QT interval.  There is evidence that large quantities of grapefruit juice alone can increase the QT interval.

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Given the vast amount of products available, and the fact that few have been completely tested for an effect on QT, it is important for healthcare providers to keep an updated record of all prescription medications, over the counter products and supplements/vitamins/herbals and check for potential interactions. Even after many years, we often become aware of interactions with old products that are potentially harmful. There is a list of drugs that could potentially interact available at www.drug-interactions.org

Are the drugs on the Conditional Risk of TdP list safe for patients with Congenital Long QT Syndrome? 

We recommend avoiding the use of these drugs, whenever possible, in patients with congenital long QT syndrome .  However, physicians with expertise in managing patients with congenital Long QT syndrome may prescribe these drugs when medically necessary.  This list includes drugs that, in some reports, have been associated with TdP and/or QT prolongation but, from the evidence that is available, we have concluded that they are unlikely to create a risk for TdP if used in usual recommended dosages.

What criteria do you use to determine how drugs get placed on each list?

The process of assessing the risk of drugs causing QT prolongation and TdP is rigorous and complex, involving multiple data sources and contingencies.
Please click here to see a description of this process.

How often is the evidence updated? Can I register to be notified when a change is made to the lists?

Our lists are monitored continually and revised frequently. If you wish, we can notify you when revisions are made. Please click here to sign up for notification of updates.

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We regularly scan the medical literature for new reports or studies suggesting that a particular drug prolongs the QT interval and/or causes TdP. Additionally, we perform ad hoc evaluations in response to inquiries sent to our website. Once we receive a report or request, we review the FDA labeling, scan the literature and mine the FDA Adverse Event Report System (AERS) database for reports suggestive of an association between the drug(s) and prolonged QT/torsades de pointes. This process often results in the drug(s) first being placed on a "watch list." Over the last three years, the lists have been updated every 1-2 months.

May I have permission to use or translate information on your site (www.QTdrugs.org, www.CredibleMeds.org) in my lecture/ paper/ book/ presentation/publication/ business report/ etc.?

We welcome anyone to use the information on our website in any way they find useful. However, we discourage printing and distributing the information because it changes frequently, and using outdated lists could be dangerous. To ensure that you have the most up-to-date information we suggest that you use the hyperlink: https://crediblemeds.org/healthcare-providers/drug-list/ .  We welcome all interested parties to use or link to the lists on our website to assure they have the most recent information.

How can I be informed about updates and how can I get them? 

Anyone can receive notice that the lists have been updated by registering with us.


For Providers: Frequently Asked Questions about drug therapy in patients with Congenital Long QT Syndrome.

Which drugs can be used to prevent arrhythmias in patients with congenital Long QT Syndrome (LQTS)? 

Beta-blockers, especially long acting agents like atenolol and nadolol, remain the mainstay of pharmacologic therapy.

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There has been a focus on understanding the genetics of LQTS in order to make rational choices for therapy. Potassium supplementation for patients with a specific HERG mutation shortens the QT and has shown promise, as well as sodium channel blockers for patients with a defective SCN5A sodium channel. However there is insufficient evidence to recommend routine use of these therapies at this time.

What antibiotics are safe in patients with congenital LQTS?

Because these drugs are not tested in LQTS patients and because there are multiple forms of LQTS, it is not possible to say that any antibiotic is "absolutely safe". There are some that clearly have been found to be dangerous and we include them on the CLQTS List. However, even if a drug is not on this list, you cannot assume that it will be safe.  We recommend using caution when administering any medication to patients with LQTS.

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The choice of antibiotic depends on the type and seriousness of the infection, infection site, resistance profile of the organism and patient's condition, so we cannot suggest a universally safe solution. Our CLQTS list contains drugs that should be avoided in patients with congenital LQTS, including some antibiotics. However, even if a certain product is not listed, it can NOT automatically be assumed to be safe. We always recommend that patients with congenital LQTS take medications only under the supervision of their physician who knows their drug therapy, their complete medical history and current medical condition. We recommend that when prescribing any medication to a patient with congenital LQTS, physicians consider potential interactions with other medications the patient is taking, their general health, including electrolyte profile, and careful observation when introducing or changing any medication.

What types of antidepressants are safe in patients with congenital LQTS? 

Prescribing for patients with congenital LQTS is a challenge. Because these drugs are not tested in LQTS patients and because there are multiple forms of LQTS with different sensitivities, it is not possible to say that any antidepressant is "absolutely safe."

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Our CLQTS List contains drugs that should be avoided in patients with congenital LQTS, including some antidepressants. However, this does not mean that a given product is automatically safe, even if it is NOT listed. We always recommend that patients with congenital LQTS take medications only under the supervision of a physician who knows the patient's drug therapy, their complete history and their current medical condition. We recommend that when prescribing any medication to a patient with congenital LQTS, physicians consider potential interactions with other medications the patient is taking, their general health, including electrolyte profile, and careful observation when introducing or changing any medication.

What types of therapies for ADHD are safe in patients with congenital LQTS? 

Because these drugs are not tested in LQTS patients and because there are multiple forms of LQTS, it is not possible to say that any drug is "absolutely safe." There is no evidence to suggest that any of the current pharmaceutical therapies for ADHD are risk-free for patients with congenital LQTS. Many of these agents are adrenergic stimulants and are presumed to be potentially dangerous.

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Our CLQTS List includes drugs that should be avoided in patients with congenital LQTS, including stimulants that have the ability to increase heart rate and blood pressure, because some patients with LQTS can develop sudden death in the presence of adrenergic stimulation. However, this does not mean that a certain product is automatically safe if it is NOT on the CLQTS list. We always recommend that patients with congenital LQTS take medications only under the supervision of their physician who knows their drug therapy, complete history and current medical condition. We recommend that when prescribing any medication to a patient with congenital LQTS, physicians consider potential interactions with other medications the patient is taking, their general health, including electrolyte profile, and careful observation when introducing or changing any medication.

Which anesthetics are safe for patients with congenital LQTS?

Many anesthetics stimulate the sympathetic nervous system and can be dangerous for those with congenital Long QT, especially Long QT1 or 2. Some anesthetics directly prolong the QT interval and are especially dangerous. It is essential that patients with congenital Long QT be treated by highly trained anesthesiologists who are familiar with this illness and the drugs that are known to prolong QT.

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Drug use in anesthesiology is a special case, since dose titration can be achieved very rapidly. We always recommend that patients with congenital LQTS take medications only under the supervision of their physician who knows their drug therapy, complete history and current medical condition. We recommend that when prescribing any medication to a patient with congenital LQTS, physicians consider potential interactions with other medications the patient is taking, their general health, including electrolyte profile, and careful observation when introducing or changing any medication.