Does Zofran Prolong QT Interval?

Long QT Syndrome (LQTS) is a disease which occurs due to the abnormality in the ion regulation inside the heart due to, which the electrical impulses fail to generate in consonance and leads to arrhythmia. The causes may be genetic which is by birth or acquired. Acquired long QT syndrome may be due to the administration of certain medicines, which interferes with the functioning of electrical activity within the heart. The symptoms of the disease are syncope (fainting), seizures or sudden death. The general treatment for the disease is prophylaxis for severe arrhythmia which may be fatal. The treatment includes avoiding drugs that causes long QT syndrome such as some medication of the class of antiallergic, antibiotic or antidepressant. Further, the patients are advised to do a change in their life style and in some patients, surgery is required.


Zofran is the brand name of generic drug ondansetron. This drug is used to manage the nausea and vomiting caused by chemotherapy, radiotherapy or surgery. The route of administration of this drug is either by mouth or by injection. The mechanism of action of this drug is the blocking of 5HT3 receptors which are found both peripherally and centrally. They are centrally present on the chemoreceptor zone which initiates the vomiting reflex. Thus, blocking this receptor will block the vomiting reflex. It is also used an off-label use in conditions such as morning sickness in pregnancy when the patient does not respond to other treatment.

Does Zofran Prolong QT Interval?

Does Zofran Prolong QT Interval?

In 2011, FDA issued warning that Zofran may induce severe arrhythmia that may have the potential to cause death. In 2012, the USFDA has issued a warning regarding the risk of intravenous ondansetron (Zofran) causing long QT syndrome. The USFDA warned that 32 mg single intravenous dose of ondansetron may affect the electrical conductivity of the heart and may cause a fatal condition called Torsades de Pointes. However, FDA also makes it clear that there is no risk in taking the lower injectable dose of the drug and also the oral dosage form. Thus, prior to give this drug to the patients the physicians are recommended to screen the patients’ medical history and the drugs the drugs administered to them presently.

It is further recommended that Zofran should be avoided in the patients with genetic long QT syndrome and screening should be done on the patients with chronic electrolytic imbalance, congestive heart failure and for medications, which may cause long QT intervals. Although the recommendations are both for oral and injection but some research authors suggest that the screening should be done only for injections and not for orals as the oral dosage form does not have the potential for causing arrhythmia as they achieve a lower plasma concentration as compared to Zofran injectables. Further, the warning contains no risk for lower intravenous dose which has more bioavailability as compared to oral Zofran form. However, caution should always be taken while giving Zofran intravenously as the effect may be additive with other drugs causing QT prolongation.


Genetic LQTS – In the genetic long QT syndrome, genes for maintaining the regulation of ions which is a pre-requisite for maintain the smooth conductivity of electrical impulses with in the brain, are mutated thus causing abnormality.

Acquired Long QT Syndrome – In acquired long QT syndrome, the patient develops this disease later in his life. This may be due to taking the medication which interferes with the electrical conductivity or when there is any serious deficiency of calcium and potassium ions. Thus the patient is advised to avoid these medications as they may trigger the symptoms or keep the electrolytes in balance.


There is a series of discussion regarding whether to screen the patients while giving injectable Zofran and oral Zofran. It seems that oral Zofran poses no risk to the patient due to low bioavailability, but while giving Zofran, even in low doses requires proper patient screening in terms of electrolytic imbalance, congestive heart failure and the concomitant drug interaction with QT interval.

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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:May 23, 2020

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