Does Cyclizine Prolong QT Interval?

There are many factors which can cause prolonged QT interval including certain medications and long QT syndrome. In males, a QT interval is regarded as prolonged if it exceeds 450 milliseconds, while in females if it exceeds 470 milliseconds. As a consequence of prolonged QT interval, one can develop the life-threatening arrhythmia known as Torsades de Pointes. It is a ventricular tachycardia syndrome which can lead to sudden cardiac death. A QT interval is displayed on an electrocardiogram (ECG), which basically represent the action potential of ventricular myocytes. It usually reflects the movements of ions across protein channels. The subsequent increase of the action potential duration causes prolonged QT interval.

What is Cyclizine?

Cyclizine is a common antihistamine that is used in treating nausea, dizziness, and vomiting to help relieve motion sickness and vertigo. Common side effects of Cyclizine include allergic reaction to the drug or its components, feeling very tired or weak and difficulties urinating. Other side effects include dry mouth and sleepiness. If you experience some of the serious complications of Cyclizine such as difficulty breathing or tightness in the chest or throat, you should see a doctor immediately. Some of the drugs under the antihistamine family that you should avoid include; Astemizole, diphenhydramine, and Terfenadine.

Does Cyclizine Prolong QT Interval?

Several antihistamine drugs have been associated with QT prolongation but Cyclizine, in particular, has not. Ondansetron, Metoclopramide, and Domperidone are other antiemetic medication which is often prescribed to relieve nausea, vomiting, and dizziness. However, Domperidone and Ondansetron are not advisable to patients with cardiac congenital disorders. Ondansetron is linked to increased risk of dose-dependent QT prolongation while Domperidone is associated with risk of serious cardiac side effects. In conclusion, Cyclizine does not prolong QT interval and would be the best choice of antiemetic for a patient with LQTS.

Important Facts About Cyclizine

Cyclizine is a type of medication given to patients with symptoms of vomiting, nausea or drowsiness due to motion sickness. It can also be given to post-operative patients with vestibular disorders. If you have taken Cyclizine, you need to be cautious when driving or handling machinery. This is because it causes drowsiness, dizziness and blurred vision which can lead to accidents. You should also not mix alcohol and Cyclizine because alcohol increases dizziness and drowsiness. For patients with risk factors such as kidney or liver disease, bladder problems and difficulty urination, Cyclizine may not be the best choice of medication as it can cause further complications. Cyclizine should not be taken in an excess dosage as it can cause poisoning. In case of an overdose, visit a physician immediately.

What is Long QT Syndrome?

Long QT syndrome (LQTS) is a congenital cardiac disorder that is associated with prolonged and increased dispersion of ventricular repolarization. This phenomenon is characterized by lengthening of the QT interval on an ECG surface. As much as this condition is hereditary, it can also be caused by a number of medications such as antiarrhythmic drugs, antihistamines, antibiotics, and antidepressants. As a matter of fact, the most common cases of LQTS are drug-induced. Some of the aforementioned types of medication interfere with the action potential of ventricular myocytes leading to QT interval prolongation. Other risk factors that increase one’s chance of developing prolonged QT interval include hypokalemia, old age, female sex, ischemia, low heart rate, low ventricular injection, and hypomagnesemia.


The normal functioning of your heart is controlled by electrical impulses, and the heart electrical system needs to recharge before every heartbeat. If you have prolonged QT interval, then your heart muscles take longer to recharge, which is evidenced on an ECG. There is a long list of drugs which has been linked to prolonged QT interval and it keeps on growing as time passes by. Antihistamines or antiemetic drugs are some of the medications that can cause drug-induced LQTS. However, not all of them have been associated with the disorder. Cyclizine is one of the commonly administered antiemetics which has not been associated with QT prolongation. That means it does not prolong QT interval.

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