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Fact Table
| Fact Table | |
|---|---|
| Formula | C18H19N3O·HCl·2H2O (ondansetron hydrochloride dihydrate); C18H19N3O (ondansetron base) |
| License | FDA approved; initial U.S. approval 1991 |
| Bioavailability | Oral mean bioavailability ~56% after an 8 mg tablet; food slightly enhances bioavailability; IV/IM systemic exposure equivalent for 4 mg injection |
| Legal status | Prescription only (Rx-only) |
| Chemical Name | (±)-1,2,3,9-tetrahydro-9-methyl-3-[(2-methyl-1H-imidazol-1-yl)methyl]-4H-carbazol-4-one, monohydrochloride, dihydrate |
| Elimination half-life | Mean ~4 hours in adult cancer patients after IV dosing; ~3.1–5.8 hours after oral dosing in healthy adults; prolonged in hepatic impairment |
| Dosage (Strength) | Oral tablets 4 mg and 8 mg; ODT 4 mg and 8 mg; oral solution 4 mg/5 mL; injection 4 mg/2 mL. Adult regimens include 24 mg once before highly emetogenic chemotherapy, 8 mg regimens for moderate chemotherapy/radiotherapy, 16 mg orally before surgery, or 0.15 mg/kg IV for chemotherapy |
| Pregnancy | Available human data do not reliably inform risk; epidemiologic findings are inconsistent; animal studies showed no fetal harm at multiples of human exposure |
| Brands | Zofran, Zofran ODT; generics available |
| Protein binding | 70–76% plasma protein bound |
| PubChem CID | 4595 (ondansetron); 59774 (ondansetron hydrochloride dihydrate/Zofran) |
| MedlinePlus | a601209; a606022 (injection) |
| ChEBI | 7773 (ondansetron); 7774 (ondansetron hydrochloride) |
| ATC code | A04AA01 |
| DrugBank | DB00904; DBSALT001248 (ondansetron hydrochloride dihydrate) |
| KEGG | D00456 (ondansetron); D00678 (ondansetron hydrochloride) |
| Routes of administration | By mouth; orally disintegrating tablet/oral solution/oral film; intravenous injection; intramuscular injection |
Zofran (ondansetron) is a prescription medication used to prevent nausea and vomiting caused by chemotherapy, radiation therapy, or surgery. It works by blocking serotonin receptors in the gut and brain that trigger the urge to vomit. As a result, it can help patients stay more comfortable during and after treatment. It is available as a regular tablet or a dissolvable tablet by prescription for adults and children.
Directions
For highly emetogenic chemotherapy (such as cisplatin), the adult dose is 24 mg taken as a single dose 30 minutes before the start of treatment. For moderately emetogenic chemotherapy, take 8 mg 30 minutes before treatment begins, then 8 mg again 8 hours later, followed by 8 mg twice daily for 1 to 2 days after completing chemotherapy. For prevention of postoperative nausea and vomiting, a single 16 mg dose is taken one hour before anesthesia.
Swallow tablets whole with water. Orally disintegrating tablets should be placed on the tongue and allowed to dissolve (no water needed). Do not exceed the recommended doses.
Ingredients
The active ingredient in Zofran is ondansetron hydrochloride dihydrate, equivalent to 4 mg or 8 mg of ondansetron per tablet. Inactive ingredients in the film-coated tablets include lactose monohydrate, microcrystalline cellulose, corn starch, silicon dioxide, magnesium stearate, hypromellose, triacetin, and titanium dioxide (the 8 mg tablet also contains ferric oxide yellow). The orally disintegrating tablets may contain aspartame, mannitol, silicon dioxide, crospovidone, magnesium stearate, sodium stearyl fumarate, and strawberry flavor.
Cautions
Before using this medication, you may want to consult a healthcare provider about the following:
- Any existing health conditions
- Any allergies
- A list of all medications currently being taken
Zofran can prolong the QT interval, a measurement of heart electrical activity. Those with heart conditions, electrolyte imbalances, or those taking other QT-prolonging drugs should be monitored.
Using Zofran with other serotonergic medications, such as SSRIs, SNRIs, fentanyl, or tramadol, may cause a potentially life-threatening condition called serotonin syndrome, with symptoms including agitation, rapid heart rate, high temperature, and muscle twitching.
In people with severe liver problems, the total daily dose should not exceed 8 mg.
Orally disintegrating tablets contain aspartame, a source of phenylalanine, and should be avoided in patients with phenylketonuria, also known as PKU.
Zofran can mask the nausea and vomiting that may be signs of a bowel obstruction. Tell a healthcare provider if unusual abdominal symptoms develop.
Contraindications
Avoid taking or using this medication if any of the following apply:
- Known allergy or hypersensitivity to ondansetron or any ingredient in Zofran
- Currently taking apomorphine, as the combination can cause a sudden severe drop in blood pressure
Side Effects
Common side effects of Zofran include:
- Headache
- Constipation
- Diarrhea
- Fatigue or general feeling of being unwell
Serious side effects can occur with Zofran. Severe allergic reactions, including anaphylaxis and bronchospasm, have been reported and require immediate medical attention.
Zofran can cause potentially dangerous changes in heart rhythm, also known as QT prolongation, that may lead to a rare but life-threatening arrhythmia.
Serotonin syndrome, a serious drug reaction causing agitation, confusion, rapid heartbeat, and muscle rigidity, has been reported in patients taking Zofran with other serotonergic drugs.
Rare cases of transient blindness lasting minutes to hours have also been reported.
Frequently Asked Questions about Zofran
What is Zofran?
Zofran is the brand name for ondansetron, a serotonin 5-HT3 receptor antagonist used to prevent nausea and vomiting. The FDA-approved oral uses are prevention of nausea and vomiting associated with highly emetogenic chemotherapy, moderately emetogenic chemotherapy, certain radiotherapy regimens, and postoperative nausea and vomiting.
How does Zofran work?
Ondansetron works by blocking serotonin at 5-HT3 receptors. Serotonin can trigger nausea and vomiting, especially after chemotherapy, radiation, or surgery, so blocking that pathway helps prevent symptoms.
How is Zofran usually taken?
Oral Zofran is available as tablets, orally disintegrating tablets, and oral solution. The timing depends on why it is being used: the first oral dose is commonly taken 30 minutes before chemotherapy, 1 to 2 hours before radiation therapy, or 1 hour before surgery. Corresponding oral formulations can be used interchangeably when the prescribed dose matches.
What doses are commonly used?
Dosing varies by indication, age, and liver function. For adults receiving highly emetogenic chemotherapy, the oral label includes a single 24 mg dose before treatment; for moderately emetogenic chemotherapy, the common oral regimen is 8 mg before chemotherapy, another 8 mg 8 hours later, then 8 mg twice daily for 1 to 2 days. In severe hepatic impairment, the total daily dose should not exceed 8 mg.
What are the most common side effects?
The most common side effects with oral ondansetron include headache, constipation, diarrhea, and fatigue or malaise. MedlinePlus also lists weakness, chills, and drowsiness among effects that can occur.
What serious side effects should people know about?
Important warnings include QT prolongation and torsade de pointes, serotonin syndrome, hypersensitivity reactions such as anaphylaxis or bronchospasm, myocardial ischemia, and the possibility of masking bowel obstruction after abdominal surgery or chemotherapy-related nausea and vomiting. Urgent evaluation is especially important for symptoms such as chest pain, fainting, irregular heartbeat, severe rash or swelling, trouble breathing, agitation, hallucinations, or muscle stiffness with fever.
Who should not take Zofran?
Zofran should not be used by people with a known hypersensitivity to ondansetron or by anyone taking apomorphine, because the combination can cause profound hypotension and loss of consciousness. The label also says to avoid ondansetron in people with congenital long QT syndrome.
What medication interactions matter most?
The most important interaction is with apomorphine, which is contraindicated. Extra caution is also needed with other serotonergic drugs, such as many antidepressants and some migraine medicines, because of serotonin syndrome risk, and with other QT-prolonging drugs or conditions that raise arrhythmia risk. Strong CYP3A4 inducers can lower ondansetron levels, but the label does not recommend a routine dose adjustment based on available data.
What should you do if you miss a dose?
Take the missed dose as soon as you remember it, but skip it if it is almost time for the next scheduled dose. Do not take two doses at the same time to make up for a missed dose.
What should people know about the orally disintegrating tablet, pregnancy, and breastfeeding?
Zofran ODT should be removed by peeling back the foil with dry hands, then placed on the tongue to dissolve; liquid is not required. In pregnancy, published studies have reported inconsistent findings and do not allow firm conclusions about safety, although postmarketing data have not identified a drug-associated risk of miscarriage or adverse maternal outcomes. For breastfeeding, available data suggest low levels in human milk and low infant exposure.
