Medically reviewed on October 21, 2016.
What is ondansetron?
Ondansetron blocks the actions of chemicals in the body that can trigger nausea and vomiting.
Ondansetron may be used for purposes not listed in this medication guide.
Before taking this medicine
You should not use ondansetron if:
you are also using apomorphine (Apokyn); or
To make sure ondansetron is safe for you, tell your doctor if you have:
an electrolyte imbalance (such as low levels of potassium or magnesium in your blood);
congestive heart failure, slow heartbeats;
a personal or family history of long QT syndrome; or
a blockage in your digestive tract (stomach or intestines).
Ondansetron is not expected to harm an unborn baby. Tell your doctor if you are pregnant.
It is not known whether ondansetron passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.
Ondansetron is not approved for use by anyone younger than 4 years old.
Ondansetron orally disintegrating tablets may contain phenylalanine. Tell your doctor if you have phenylketonuria (PKU).
How should I take ondansetron?
Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Ondansetron can be taken with or without food.
The first dose of ondansetron is usually taken before the start of your surgery, chemotherapy, or radiation treatment. Follow your doctor's dosing instructions very carefully.
Take the ondansetron regular tablet with a full glass of water.
To take the orally disintegrating tablet (Zofran ODT):
Keep the tablet in its blister pack until you are ready to take it. Open the package and peel back the foil. Do not push a tablet through the foil or you may damage the tablet.
Use dry hands to remove the tablet and place it in your mouth.
Do not swallow the tablet whole. Allow it to dissolve in your mouth without chewing.
Swallow several times as the tablet dissolves.
To use ondansetron oral soluble film (strip) (Zuplenz):
Keep the strip in the foil pouch until you are ready to use the medicine.
Using dry hands, remove the strip and place it on your tongue. It will begin to dissolve right away.
Do not swallow the strip whole. Allow it to dissolve in your mouth without chewing.
Swallow several times after the strip dissolves. If desired, you may drink liquid to help swallow the dissolved strip.
Wash your hands after using Zuplenz.
Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.
Store at room temperature away from moisture, heat, and light. Store liquid medicine in an upright position.
What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
Overdose symptoms may include sudden loss of vision, severe constipation, feeling light-headed, or fainting.
What should I avoid while taking ondansetron?
Ondansetron may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.
Ondansetron side effects
Call your doctor at once if you have:
severe constipation, stomach pain, or bloating;
fast or pounding heartbeats;
jaundice (yellowing of the skin or eyes);
blurred vision or temporary vision loss (lasting from only a few minutes to several hours);
Common side effects may include:
diarrhea or constipation;
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
What other drugs will affect ondansetron?
Ondansetron can cause a serious heart problem, especially if you use certain medicines at the same time, including antibiotics, antidepressants, heart rhythm medicine, antipsychotic medicines, and medicines to treat cancer, malaria, HIV or AIDS. Tell your doctor about all medicines you use, and those you start or stop using during your treatment with ondansetron.
Taking ondansetron while you are using certain other medicines can cause high levels of serotonin to build up in your body, a condition called "serotonin syndrome," which can be fatal. Tell your doctor if you also use:
medicine to treat depression;
medicine to treat a psychiatric disorder;
a narcotic (opioid) medication; or
medicine to prevent nausea and vomiting.
This list is not complete and many other drugs can interact with ondansetron. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Copyright 1996-2018 Cerner Multum, Inc. Version: 13.01.
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