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Ondansetron - An Anti-Sickness Medicine

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Ondansetron is one of the medications most commonly used to prevent nausea and vomiting. Learn about its uses, side effects, dosage, warnings, precautions, and more.

Medically reviewed by

Dr. Mohammad Rajja

Published At December 19, 2022
Reviewed AtMarch 13, 2023

What Is Ondansetron?

Ondansetron is a serotonin receptor antagonist medication used to prevent and treat nausea and vomiting. The antiemetic is considered effective and safe against nausea and vomiting of various etiologies. The drug is FDA-approved and appears on the World Health Organization’s (WHO) List of Essential Medicines with other antiemetics, like Dexamethasone and Metoclopramide.

What Is Ondansetron Used For?

Typically, Ondansetron is used to prevent chemotherapy-induced and radiation-induced nausea and vomiting. The antiemetic is also recommended for the prevention of postoperative nausea and vomiting. Doctors may prescribe Ondansetron to prevent nausea and vomiting associated with pregnancy. Ondansetron may be used to treat cyclic vomiting syndrome in children acutely. Ondansetron is considered first-line therapy for the treatment of chemotherapy-induced and radiation-induced nausea and vomiting.

How Does Ondansetron Work?

Ondansetron is a selective 5-HT3 serotonin-receptor antagonist that acts centrally and peripherally to prevent and treat nausea and vomiting. The antagonist prevents the binding of serotonin released from the intestinal enterochromaffin cells to 5-HT3 receptors on the adjacent vagal afferent nerves. The onset of action is 30 minutes, with peak plasma concentration between 60 and 120 minutes. The effect of Ondansetron may last for up to 12 hours. Ondansetron is metabolized in the liver with hydroxylation and is exerted primarily in the urine.

How to Use Ondansetron?

Ondansetron is a rapidly disintegrating tablet and an oral solution to take by mouth. The drug may be taken with or without food.

  • Chemotherapy - The first dose of Ondansetron is usually taken 30 minutes before the start of chemotherapy. Additional doses may be given after the end of treatment.

  • Radiation Therapy - The antiemetic is given one to two hours before the start of radiation therapy. It may be required to continue Ondansetron for a few more days.

  • Surgery - Ondansetron is usually given one hour before the surgery to prevent postoperative nausea and vomiting. The rapidly disintegrating tablets should be allowed to dissolve in the mouth and be swallowed. The liquid medicine should be measured with a dosing spoon or syringe. If you miss a dose, you should take it as soon as you remember. Do not take double doses, as it may cause adverse effects. Ondansetron should be stored at room temperature, away from heat, light, and moisture.

What Is the Dosage of Ondansetron?


Ondansetron ADULT DOSAGE


CHILDREN Dosage of Ondansetron

What Are Precautions to Be Taken When Using Ondansetron?

  • Allergy - Ondansetron should be avoided by people who have had allergic reactions to it or any of its components. The drug should not be used if you are allergic to similar medicines such as Dolasetron, Granisetron, or Palonosetron.

  • Pregnancy and Breastfeeding - Ondansetron should be used with caution during pregnancy as there is an increased risk of cleft lip and palate, especially during the first trimester of pregnancy. Breastfeeding mothers should avoid taking Ondansetron as it may harm the baby.

  • Liver Disease - Ondansetron is extensively metabolized by the liver. There may be decreased plasma clearance of Ondansetron in patients with impaired hepatic function.

  • Heart Failure - The use of Ondansetron in patients with heart failure can increase the risk of arrhythmias.

  • Geriatrics - People over 65 years have decreased metabolism leading to delayed drug excretion. This can increase the risk of side effects.

  • Alcohol - Taking alcohol with Ondansetron may worsen the side effects such as drowsiness or dizziness.

  • Long QT syndrome - Ondansetron should be avoided in patients with congenital long QT syndrome. It is recommended to do ECG monitoring and potassium and magnesium monitoring in patients with electrolyte abnormalities or bradyarrhythmias.

  • Children - Ondansetron should not be used in children younger than four.

  • Mind Alertness - Ondansetron may impair thinking and reactions and should be avoided when driving or handling machinery.

Does Ondansetron Affect Serotonin Levels?

The use of Ondansetron can increase serotonin levels in the body. This can cause a life-threatening condition called serotonin syndrome. A high level of serotonin can cause agitation, delirium, and hallucinations. It can also cause sweating, rapid heartbeat, muscle stiffness, tremors, seizures, jerky muscle movements, and coma. Serotonin syndrome can occur using Ondansetron alone or with another drug that affects serotonin levels.

What Are the Side Effects of Ondansetron?

Some of the side effects of Ondansetron may include,

  • Headaches.

  • Fatigue.

  • Constipation.

  • Drowsiness.

  • Diarrhea.

  • Dizziness.

  • Fever and chills.

  • Anxiety.

Serious side effects include

  • Tingling or numbness.

  • Temporary vision loss.

  • Yellowing of the skin.

  • Fast and pounding heartbeats.

  • Hallucinations.

  • Trouble breathing.

  • Loss of coordination.

  • Slow heart rate.

  • Palpitations.

  • Severe allergic reactions may cause symptoms like flushing, tongue and throat swelling, dizziness, trouble breathing, or coughing.

What Are the Interactions of Ondansetron?

Certain drugs, foods, dyes, and supplements can change the effectiveness or increase the risk of serious side effects when taken with Clarithromycin.

Drug Interaction:

  • Apomorphine.

  • Dronedarone.

  • Adderall.

  • Benadryl.

  • Metoprolol.

  • Paracetamol.

  • Cymbalta.

  • Lyrica.

  • Acetaminophen.

  • Antidepressants such as Fluoxetine and Paroxetine.

  • Duloxetine.

  • Lithium.

  • Anti-seizure drugs such as Phenytoin or Carbamazepine can decrease the effectiveness of Ondansetron.

  • Tuberculosis drugs such as Rifampin, Rifabutin, or Rifapentine can make Ondansetron less effective.

Interaction with Disease:

  • QT Interval Prolongation - Ondansetron should be avoided in patients with congenital long QT syndrome. ECG (electrocardiography) monitoring is recommended in patients with hypokalemia or bradyarrhythmias for QT interval prolongation.

  • Liver Disease - Therapy with Ondansetron should be administered with caution and at reduced dosages in patients with liver disease as there may be decreased plasma clearance and prolonged half-life.

  • Phenylketonuria - Orally disintegrating tablets of Ondansetron contain phenylalanine which can cause dangerous effects on people with phenylketonuria and hence, should be avoided.

  • Gastric Distension - Ondansetron may mask the symptoms of stomach and intestinal problems, especially in patients who have had recent stomach surgery.


Ondansetron may be used alone or with other medications to prevent nausea and vomiting caused by chemotherapy or radiation therapy or may be given to treat nausea and vomiting after surgery. It works by blocking serotonin in the brain, which causes vomiting.

Frequently Asked Questions


How to Take Ondansetron 8MG?

Ondansetron is used in cases of nausea and vomiting. In most cases of cancer treatment, while doing radiation therapy, Ondansetron is prescribed. For adults and children above 12 years of age, Ondansetron is prescribed, initially at the dose of 8 mg before starting the cancer treatment. An 8 mg dose is given again after eight hours of the 1st dose. The dose is then 8 mg after 12 hours for one to two days.


How Long Until Ondansetron Is Out of One’s System?

Ondansetron has a half-life of three to four hours in healthy young adults, but this can be increased to six to eight hours in older adults. This means it takes the body three to four hours to eliminate half a dose of Zofran from the body, so the entire amount should be eliminated in 15 to 20 hours.


How Many Ondansetron Tablets Can Be Taken?

For adults and children, the first dose of Ondansetron can be taken in a dose of 8 mg 30 minutes before the treatment starts and the 2nd dose of 8 mg after eight hours of the 1st dose. The dose is then 8 mg after 12 hours for one to two days.


Is Ondansetron Safe in Pregnancy?

Most studies suggest that there is not much risk associated with taking Ondansetron during pregnancy. Very few cases (less than one percent) may show an increase in the chances of a cleft palate (an opening in the roof of the mouth that can be corrected with surgery) or a heart defect.


How Can Ondansetron Cure Nausea and Vomiting?

Ondansetron is a group of medicines that belongs to serotonin 5-HT3 receptor antagonists. The work of Ondansetron starts by blocking the action of serotonin, which is a natural substance that may cause nausea and vomiting.


How Fast Can One Push Ondansetron?

The recommended intravenous dose for Ondansetron is 8 mg, administered as a slow injection (administered in at least 30 seconds) or as an infusion over 15 minutes just before the treatment.


How Does Ondansetron Cause QT Prolongation?

Qt interval prolongation is one of the most important side effects of Ondansetron and increases the risk of torsade de pointes (a type of fast heart rhythm or tachycardia). In addition to this, cardiac arrhythmia has also been reported with the administration of serotonin receptor inhibitors.


How Quickly Does Ondansetron Work?

Ondansetron is used in cases of nausea and vomiting. In most cases of cancer treatment, while doing radiation therapy, Ondansetron is prescribed. Ondansetron starts to work usually within 30 minutes to one hour of the intake.


How to Get Prescribed Ondansetron?

In case of nausea or vomiting, especially during cancer treatment, Ondansetron is prescribed. It can only be taken with the prescription of a doctor.


How to Pronounce Ondansetron?

Ondansetron isa class of medicine that is used in cases of nausea and vomiting. It is pronounced as awn-dan-suh-trawn.


How to Take Ondansetron odt 4mg Tablets?

It can be taken on an empty stomach or full. But the best results are seen on an empty stomach, an hour before, or two hours after the food.


How to Use an Ondansetron Oral Solution ip?

Put the soluble film immediately below the tongue. It gets dissolved within four to 20 seconds.


How Does Ondansetron Cure Nausea?

Ondansetron is a class of medication that belongs to the serotonin 5-HT3 antagonist. It works by blocking the action of serotonin.


How Much Does Ondansetron Cost?

The cost of Ondansetron can vary slightly at some places and in different brands. Approximately OD ondansetron 4mg tablet costs 50 rupees per strip.


How Much Ondansetron Can a Dog Take?

It can be given in doses of 0.5 to 1 mg/kg up to three times a day. 4 mg for a small dog and 8 mg for a large dog.
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Dr. Mohammad Rajja
Dr. Mohammad Rajja

General Practitioner


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