Heart Rhythm Problems
Zofran ODT can affect the electrical activity of the heart and may cause QT prolongation.
In rare cases, this can lead to a serious abnormal heart rhythm called torsades de pointes.
The risk may be higher if you:
- Have congenital long QT syndrome
- Have heart failure
- Have a slow or abnormal heartbeat
- Have low potassium or magnesium levels
- Take other medications that prolong the QT interval
Seek medical attention if you develop a fast or irregular heartbeat, severe dizziness, or fainting.
Serotonin Syndrome
Zofran ODT can rarely contribute to serotonin syndrome, especially when it is taken with other medications that increase serotonin.
These may include some antidepressants, tramadol, lithium, fentanyl, and certain other medicines.
Seek medical attention if you develop symptoms such as:
- Agitation or confusion
- Fast heartbeat
- Sweating
- Fever
- Muscle stiffness
- Tremors
- Poor coordination
Serotonin syndrome can be serious and requires prompt treatment.
Allergic Reactions
Serious allergic reactions can occur.
Seek emergency medical attention if you develop:
- Hives
- Severe rash
- Swelling of the face, lips, tongue, or throat
- Difficulty breathing or swallowing
People who have had an allergic reaction to another 5-HT3 receptor antagonist may also be at increased risk.
Liver Problems
Ondansetron is processed mainly by the liver.
If you have severe liver impairment, your dose may need to be limited.
Tell your healthcare provider if you have liver disease before starting Zofran ODT.
Kidney Problems
Kidney impairment usually does not require a dose adjustment of ondansetron.
However, tell your healthcare provider if you have significant kidney disease so your overall treatment can be monitored appropriately.
Phenylketonuria (PKU)
Many ondansetron orally disintegrating tablets contain aspartame, which provides phenylalanine.
If you have phenylketonuria (PKU), check the product label or ask your pharmacist how much phenylalanine your specific tablet contains.
Constipation and Bowel Problems
Zofran ODT can cause constipation.
It may also hide signs of a slowing or blockage of the intestines, especially after abdominal surgery or during chemotherapy.
Contact your healthcare provider if you develop:
- Severe abdominal swelling
- Persistent constipation
- Severe stomach pain
- Vomiting
- Little or no bowel movement
These symptoms may require medical evaluation.
Drug Interactions
Tell your healthcare provider about all prescription medications, over-the-counter products, vitamins, supplements, and herbal products you use.
Zofran ODT can interact with several medications.
Do not use ondansetron with apomorphine, because the combination can cause severe low blood pressure and loss of consciousness.
Extra caution is also needed with serotonergic medicines and drugs that can prolong the QT interval.
Pregnancy
Tell your healthcare provider if you are pregnant or planning to become pregnant.
Available human pregnancy data have not established a clear drug-related risk of major birth defects or miscarriage.
Your healthcare provider will consider your symptoms and overall health before recommending treatment.
Breastfeeding
Tell your healthcare provider if you are breastfeeding.
There is limited information about ondansetron in human breast milk.
Your healthcare provider will consider the benefits of breastfeeding, your need for treatment, and any potential risk to the nursing infant.
Dizziness and Vision Changes
Ondansetron may occasionally cause dizziness or vision changes.
Avoid driving or operating machinery if you feel dizzy or your vision is affected.
Rare cases of temporary vision loss have been reported, mainly with intravenous ondansetron rather than oral tablets.
Older Adults
Older adults may be more likely to have heart rhythm problems or take other medications that affect the QT interval.
Your healthcare provider may recommend closer monitoring if you have heart disease, electrolyte problems, or take several medications.
When to Seek Medical Attention
Seek prompt medical attention if you develop fainting, an irregular heartbeat, severe allergic symptoms, severe confusion, muscle rigidity, severe abdominal swelling, or other unusual or worsening symptoms.
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