Zofran dosage, forms, and strengths

Zofran is a brand-name prescription drug that prevents nausea and vomiting in people undergoing chemotherapy, radiation therapy, or surgery. It is currently available as a generic drug only. 

Zofran is an antiemetic or anti-nausea drug that contains the active ingredient ondansetron. It works as a 5-HT3 receptor antagonist that blocks the effects of a chemical called serotonin in the brain. Serotonin stimulates receptors in the chemoreceptor trigger zone, an area of the brain that controls nausea and vomiting. By blocking serotonin, ondansetron helps calm the brain’s nausea reflex. 

Zofran is often taken as a tablet with or without food. However, the dosage of Zofran can vary depending on the cause of nausea. It’s important to follow the dosage instructions of your healthcare provider to ensure you use Zofran safely and effectively. 

Continue reading to learn more about Zofran’s dosage and administration. 

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Zofran forms and strengths

Zofran is currently sold as a generic medication that comes as a regular tablet, orally disintegrating tablet (ODT), and oral solution. Brand-name dosage forms have been discontinued. In a clinical setting, generic Zofran is also available as an injectable solution given intravenously (IV) or intramuscularly (IM). An ondansetron soluble film was once marketed under the brand name Zuplenz, but this brand and format are no longer available. 

• Tablet: 4 mg, 8 mg, and 24 mg

• Orally disintegrating tablet: 4 mg and 8 mg

• Oral solution: 4 mg per 5 mL

• Injectable solution: 2 mg per mL

Zofran dosage for adults

Ondansetron is approved by the Food and Drug Administration (FDA) to prevent nausea and vomiting in people undergoing highly or moderately emetogenic (nausea-inducing) chemotherapy or radiation therapy. Ondansetron is also approved to prevent nausea or vomiting after surgery. 

• Standard dosage for adults: 8 to 24 mg given in a single dose before chemotherapy, radiation therapy, or before anesthesia and sometimes every eight to 12 hours for one to two days afterward

Maximum dosage for adults: 24 mg per day

Dosage sources include Epocrates, DailyMed, and PDR

Zofran dosage for preventing nausea caused by cancer chemotherapy

Chemotherapy commonly causes nausea and vomiting as side effects. The risk of nausea and vomiting varies depending on the medication, dosage, and treatment schedule. Chemotherapy medications may be categorized as high, moderate, low, or minimal risk when it comes to potential nausea and vomiting. 

For example, highly emetogenic drugs are medications that have a high risk of causing nausea and vomiting, with more than 90% of cancer patients experiencing these side effects without preventive treatment. Examples include cisplatin, dacarbazine, and high-dose cyclophosphamide. A high dose of ondansetron is typically given 30 minutes before highly emetogenic chemotherapy. 

Moderately emetogenic drugs are medications with a moderate risk of causing nausea and vomiting, with 30% to 90% of cancer patients experiencing these side effects without preventive treatment. Examples include carboplatin, doxorubicin, and oxaliplatin, among others. 8 mg of ondansetron is given before and 8 hours after moderately emetogenic chemotherapy, and then 8 mg is taken every 12 hours for up to two days after treatment. 

Zofran dosage for preventing nausea caused by radiation therapy

Radiation treatment for cancer often causes nausea and vomiting as a side effect, especially if the radiation is focused on the brain, liver, or gastrointestinal tract. There are different types of radiotherapy, including internal, external, and systemic radiation. The total radiation dose is usually divided into smaller doses called fractions to reduce side effects. 

The recommended dosage regimens can vary depending on the type of radiation and where it’s focused.

• Radiotherapy (general): 8 mg orally three times daily

• Total body irradiation: 8 mg one to two hours before each fraction of radiotherapy 

• Single high-dose abdominal radiation: 8 mg one to two hours before radiation treatment. Then, 8 mg every eight hours after the first dose for one to two days following treatment

• Fractionated abdominal radiation: 8 mg one to two hours before radiation treatment. Then, 8 mg every eight hours after the first dose for every day that treatment is given

Zofran dosage for the prevention of postoperative nausea

Postoperative nausea and vomiting (PONV) is a common side effect of anesthesia, generally affecting around 20% to 30% of people undergoing surgery. The risk of severe nausea and vomiting may be higher after certain procedures, such as abdominal surgery. 

In susceptible patients, nausea and vomiting typically occur within the first 24 hours after surgery in the postanesthesia care unit. Nausea and vomiting after surgery can be uncomfortable and sometimes lead to a prolonged hospital stay. Ondansetron may be given before anesthesia to prevent PONV, depending on the person’s risk for nausea.

• PONV in adults: 16 mg single dose given one hour before anesthesia

Zofran dosage for children

Ondansetron oral tablets can be given to prevent nausea and vomiting due to chemotherapy in children four years of age and older. In children and infants six months and older, ondansetron is given intravenously to prevent nausea and vomiting caused by chemotherapy. 

For postoperative nausea and vomiting, IV ondansetron may be given to children and infants as young as one-month-old. However, the dosage varies depending on the individual’s weight. Ondansetron is typically given as a single IV dose immediately before or after surgery in children and infants to prevent postoperative nausea and vomiting. 

Zofran dosage restrictions

Ondansetron is not right for everyone. The use of ondansetron should be avoided in people with a known allergy to any ingredients in the medication. Signs and symptoms of a serious allergic reaction may include hives, rash, swelling of the throat or face, and difficulty breathing.

Ondansetron should not be taken with Apokyn (apomorphine), a drug prescribed to treat Parkinson’s disease. Mixing these drugs can lead to low blood pressure (hypotension) and unconsciousness. Ondansetron may also interact with other medications, including serotonergic drugs and medications that affect liver metabolism. 

Other warnings and precautions of ondansetron include:

• Heart rhythm problems (QT interval prolongation and Torsades de Pointes), especially in people with electrolyte imbalances, heart failure, or other heart problems

• Serotonin syndrome, is a potentially serious condition that may require treatment, especially in people who are taking serotonergic drugs

• Ischemic heart disease or reduced blood flow to the heart muscle, leading to chest pain or tightness in the chest

• Gastrointestinal problems

• Phenylketonuria (PKU) due to the phenylalanine content of ondansetron ODT

Ondansetron is metabolized by the liver. Therefore, people with severe liver disease (severe hepatic impairment) may be restricted to a lower dose of 8 mg of ondansetron per day. People with kidney disease (renal impairment) generally do not require a dosage adjustment. 

How to take Zofran

Ondansetron can be taken orally as a tablet, orally disintegrating tablet, or oral solution. It can be taken with or without food, and the effects should start within 30 minutes to an hour after oral administration.

The dosage will vary depending on a person’s overall condition and what the medication is being used for. IV and IM ondansetron will be administered in a hospital or clinical setting. Ondansetron should only be taken as directed by a doctor or healthcare provider.

Tablet

• Take oral tablets with a full glass of water

• Store tablets at room temperature (36°F to 86°F) in a light-resistant container

Orally disintegrating tablet

• Do not open the blister pack containing the tablet until you are ready to take it

• Do not push the tablet through the foil backing to remove it

• With dry hands, peel back the foil backing of one blister and gently remove the tablet

• Place the tablet on the tongue. Allow the tablet to dissolve fully. It will dissolve in seconds

• Swallow what’s left of the tablet with saliva

• Store ondansetron orally disintegrating tablets at room temperature (36°F to 86°F)

Oral solution

• Make sure to keep the bottles upright and store them between 59°F and 86°F

• To protect the oral liquid form from light exposure, keep the bottles inside their cartons

Zofran dosage FAQs

How long does it take Zofran to work?

Ondansetron generally starts working within 30 minutes to an hour. It reaches peak levels in the blood at around one and a half hours after taking oral administration. It may take a longer time for Zofran oral tablets to work than Zofran ODT or IV forms. 

How long does Zofran stay in your system?

How long ondansetron stays in your system depends on various factors, including age and overall health. The half-life of an 8-mg tablet or IV dose of ondansetron is around three to four hours. However, in older adults with decreased liver function, the half-life may be around five and a half hours. As it takes four to five half-lives for a drug to be cleared from the body, ondansetron could stay in your system for up to 20 hours after a dose. 

Why do you push Zofran slowly?

Ondansetron injectable solution is infused slowly to prevent the risk of side effects. Injecting the medication could increase the risk of side effects such as headache, dizziness, and skin flushing. The recommended time frame for administering a dose of ondansetron is typically over 15 minutes in adults and two to five minutes in pediatric patients. 

What happens if I miss a dose of Zofran?

If you miss a dose of ondansetron, take it as soon as you remember unless it's almost time for your next dose. In that case, skip the missed pill and continue your regular schedule. Do not take a double dose to make up for the missed one. If you're unsure what to do, consult your doctor or pharmacist for guidance on managing additional doses.

Can you overdose on Zofran?

Yes, it is possible to overdose on ondansetron. An ondansetron overdose can be a serious medical emergency that can cause temporary vision loss, constipation, low blood pressure, and fainting. Children who overdose on Zofran are especially vulnerable to serotonin syndrome, a potentially dangerous condition that can cause drowsiness, rapid heart rate, increased sweating, and seizures. Seek immediate medical help if you suspect an overdose. 

What interacts with Zofran?

There are several possible drug interactions between ondansetron and other prescription medications. The concomitant use of other medicines with ondansetron could lead to severe adverse effects and may need to be avoided or monitored. For example, using serotonergic drugs, including SSRI antidepressants and certain migraine medications, may increase the risk of serotonin syndrome. 

The use of ondansetron should be monitored while using drugs that can cause an irregular heartbeat as a side effect. For example, antiarrhythmics are drugs that may increase the risk of QT prolongation or an abnormal heart rhythm while taking Zofran. 

Certain medications can affect the metabolism of ondansetron in the liver. Some drugs, such as certain antibiotics and antifungals, can cause ondansetron to build up, leading to an increased risk of serious side effects. Other medicines can cause ondansetron to break down, reducing its effectiveness. 

Tell your healthcare provider if you take other medications, including prescription drugs, over-the-counter medicine, or herbal supplements. 

Is it safe to take Zofran during pregnancy?

Various studies have shown that the use of Zofran is not linked to abnormal pregnancy outcomes. However, a small number of studies have found that ondansetron may have a small risk of heart problems, including septum defects, in an unborn baby. It is important to consult a healthcare provider for more information and medical advice on treatment options for nausea during pregnancy. 

Related resources for Zofran dosages:

• Consensus guidelines for the management of postoperative nausea and vomiting, Anesthesia & Analgesia

• Drug-induced QT prolongation, U.S. Pharmacist

• Nausea and vomiting related to cancer, National Cancer Institute

• Ondansetron drug summary, Prescriber’s Digital Reference

• Pharmacokinetics and bioequivalence testing of generic ondansetron preparations in healthy Thai male volunteers, International Journal of Clinical Pharmacology and Therapeutics

• Zofran, Epocrates

• Zofran ondansetron 4 mg orally disintegrating tablet prescribing information, U.S. National Library of Medicine

• Zofran ondansetron hydrochloride film-coated tablet prescribing information, U.S. National Library of Medicine