What Medications Can Cause Long QT Syndrome?

Long QT Syndrome (LQTS) is a condition in which the heart fails to supply the blood efficiently to various parts of the body. This is due to the abnormal ion regulation within the heart essential for optimizing the conduction of electrical impulses. This results in the fast and non-rhythmic heartbeat and if such a situation continues for a long time, it may result in cardiac arrest or sudden death. The syndrome may be either acquired or congenital and it may occur due to the use of certain medication, which interferes with the regulation of ions in the heart. There are certainly other causes such as low concentration of calcium or potassium in the blood, which is also essential for maintaining the cardiac rhythm.

What Medications Can Cause Long QT Syndrome?

What Medications Can Cause Long QT Syndrome?

Long QT syndrome is divided in to two types on the basis of occurrence of this condition. In congenital LQTS, the syndrome is present at the time of birth as the genes which are responsible for maintaining the ion balance in the heart becomes abnormal. In acquired long QT syndrome, the patient suffers from this syndrome later in his life. The cause of acquired LQTS is low calcium and low potassium in the blood and also attributed to various medications which interfere with the ion exchange within the heart.

In the acquired long QT syndrome, the reason is due to the blockage of hERG channel, which can be due to certain medications. These medications, due to their side effects are either withdrawn from the market or contraindicated in the people with such conditions.

Following are the medications which are implicated in the prolongation of QT interval:

  1. Antiarrhythmic agents such as quinidine block both the sodium and potassium channels. Further, drugs such as dofetilide and sotalol carry the risk of prolonging QT interval. Disopyramide is also contraindicated in the patients with cardiac problems.
  2. Cisapride, a drug used for GERD caused a prolongation in QT interval and is followed by the withdrawal from the US market because of this life-threatening side effect. Chloroquine can also prolong the QT interval and cause long QT syndrome.
  3. Some of the antibiotics are also known for increase in the QT interval. Clarithromycin and erythromycin have the side effects of prolonging QT interval.
  4. Antihistamines such as loratadine and diphenhydramine also trigger the prolonged QT interval.
  5. Tricyclic antidepressants are known for prolonging the QT interval and cause long QT syndrome. The drugs such as nortriptyline, amitriptyline, desipramine also prolongs QT interval. Further to this, the other commonly used antidepressants such are citalopram, escitalopram and venlafaxine are also included in this category.
  6. Drugs such as quetiapine, olanzapine and amisulpride also interfere with the QT interval.
  7. Antiprotozoal drug, pentamidine also causes prolong QT interval.


Heart has the function to maintain the blood flow to various organs. In long QT syndrome, this capacity of the heart is greatly reduced, and the results start appearing in the form of symptoms. When the blood supply is reduced, there is an overall fatigue in the body. Further, the organs mostly affected are brain. When the blood supply is lowered in brain, the patient starts feeling fainted, a condition known as syncope. Further, there are seizures like effects in the brain. The condition is diagnosed when the patient experiences cardiac symptoms. Further, in some cases, the condition remains undiagnosed as there are no symptoms and is founded during routine checkup.


Congenital long QT syndrome is due to the mutation in genes controlling the flow of ions in the heart. However, acquired LQTS is generally due to the blockage of the flow of ions. Certain drugs are involved in such blockage. These drugs are either removed from the market or, if they are present, are contraindicated in the patients with long QT syndrome. These drugs are from various therapeutic categories and include the antipsychotics, antidepressants, gastrointestinal drug, antimicrobials, antimalarials, antiprotozoal and antiarrhythmic drugs. As the LQTS has life-threatening implications thus such drugs should be used with utmost care in the patients with long QT syndrome.

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Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:April 19, 2019

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