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Generic Name: ondansetron

Brand Names: Zofran, Zofran ODT, Zuplenz

Drug Class: Antiemetics, Selective 5-HT3 Antagonist

What is ondansetron, and what is it used for?

Ondansetron is an antiemetic medication prescribed to prevent nausea and vomiting caused by cancer treatments such as chemotherapy and radiation, and anesthetic medications used during surgeries. Ondansetron is also used to treat extreme and persistent nausea and vomiting during pregnancy, and itching caused by opioid medications and certain specific conditions.

Ondansetron works by blocking the activity of serotonin, a chemical messenger (neurotransmitter) that is involved in inducing nausea and vomiting. Chemotherapy and radiotherapy are associated with the release of serotonin in the gastrointestinal (GI) tract, which stimulate serotonin 5-HT3 receptors on nerve cells (neurons), triggering the vomiting reflex.

Ondansetron prevents the vomiting reflex by selectively blocking the serotonin 5-HT3 receptors on the vagus nerve which regulates GI activity. Ondansetron also blocks 5-HT3 receptors in the area postrema in the brain stem, which induces vomiting in response to serotonin and toxins. Ondansetron is also used to treat itching from certain liver and kidney diseases, which is mediated by serotonin.

The uses of ondansetron include the following:

Adult

• Prevention (prophylaxis) of chemotherapy-induced nausea and vomiting
• Radiation-induced nausea and vomiting
• Post-operative nausea and vomiting

Off-label uses include:

• Itching due to liver disease (cholestatic pruritus)
• Itching due to kidney disease (uremic pruritus)
• Itching caused by spinal opioid therapy
• Itching from rosacea, a skin condition
• Severe nausea and vomiting in pregnancy (hyperemesis gravidarum)

Pediatric

• Prevention (prophylaxis) of chemotherapy-induced nausea and vomiting
• Post-operative nausea and vomiting

Warnings

• Do not administer with apomorphine; the combination has been reported to cause severe drop in blood pressure and loss of consciousness
• Do not administer to patients who are hypersensitive to ondansetron or any of its components
• Do not administer to patients who have had hypersensitivity to other selective 5-HT3 antagonists
• Hypersensitivity can cause severe reactions including anaphylaxis and bronchospasm; discontinue immediately and institute supportive and symptomatic therapy
• Reduce dose in patients with impaired liver function
• Ondansetron can cause ECG changes; ECG should be monitored in patients with congestive failure, electrolyte imbalance or slow, irregular heartbeat (bradyarrhythmia)
• Ondansetron can increase serotonin levels and lead to serotonin syndrome; concomitant use with drugs that increase serotonin levels can increase the risk, and in some cases, has been fatal. Drugs that are serotonergic include selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), monoamine oxidase inhibitors (MAOIs), lithium, fentanyl, tramadol, methylene blue IV, and mirtazapine
• Reduced blood flow to the heart muscle (myocardial ischemia) has been reported in patients treated with ondansetron
• Ondansetron does not stimulate the muscle contraction that move gastrointestinal contents (peristalsis); should not be used instead of nasogastric suction
• Ondansetron may mask progressive lack of movement in the intestines (ileus) or gastric distention in patients who are undergoing abdominal surgery or experiencing chemotherapy-induced nausea and vomiting; monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction
• Ondansetron orally disintegrating tablets contain phenylalanine, an amino acid; should be used with caution in patients with phenylketonuria, an inherited disorder that causes phenylalanine buildup in the body

What are the side effects of ondansetron?

Common side effects of ondansetron include:

• Headache
• Feeling unwell (malaise)
• Fatigue
• Constipation
• Low tissue oxygen levels (hypoxia)
• Drowsiness
• Dizziness
• Gynecological disorder

Less common side effects of ondansetron include:

• Fever
• Diarrhea
• Anxiety
• Urinary retention
• Elevated liver function test results
• Injection site pain, redness and burning sensation
• Itching (pruritus)
• Cold sensation
• Prickling sensation (paresthesia)

Rare side effects of ondansetron may include:

• Nausea and vomiting
• Abnormal liver function
• Specific liver enzyme abnormalities
• Liver tissue death (necrosis)
• Irregular heart rhythm conditions (arrhythmias) including
  • Premature ventricular contractions
  • Atrial fibrillation
  • Ventricular and supraventricular tachycardia
  • Abnormally slow heartbeat (bradycardia)
• Abnormal ECG
• Palpitations
• Reduced blood flow to the heart muscle (myocardial ischemia), predominantly with intravenous ondansetron
• Fainting (syncope)
• Hiccups
• Neurologic reaction with spasm in eye muscle (oculogyric crisis), sometimes with other involuntary muscle movements
• Transient dizziness during or shortly after intravenous infusion
• Transient blindness predominantly with IV infusion
• Transient blurred vision
• Joint pain (arthralgia)
• Flushing
• Hives (urticaria)
• Serious skin reactions that can be life-threatening such as:
  • Stevens-Johnson syndrome
  • Toxic epidermal necrolysis
• Severe hypersensitivity reactions (anaphylaxis) including:
• Swelling of tissue under skin and mucus membranes (angioedema)
• Bronchospasm
  • Swelling of the voice box (laryngeal edema)
  • Spasm of the voice box (laryngospasm)
  • Whistling sound while breathing (stridor)
  • Shortness of breath (dyspnea)
  • Low blood pressure (hypotension)
  • Cardiopulmonary arrest
  • Shock

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug.

Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

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What are the dosages of ondansetron?

Injectable Solution

• 2mg/mL

Tablet

• 4mg
• 8mg
• 24mg

Oral Solution

• 4mg/5mL

Oral Soluble Film

• 4mg
• 8mg

Orally Disintegrating Tablets

• 4mg
• 8mg

Adult

Postoperative Nausea and Vomiting

Prophylaxis

• 4 mg intravenously/intramuscular immediately before anesthesia or after the procedure or 16 mg orally 1 hour before anesthesia; patients over 80 kg may need an additional 4 mg intravenously

Radiation-Induced Nausea and Vomiting

Prophylaxis

• Total body radiation therapy: 8 mg orally 1-2 hours before radiation therapy; administered each day
• Single high-dose fraction therapy to the abdomen: 8 mg orally 1-2 hours before radiation therapy; administer subsequent doses every 8 hours after first dose 1-2 days after completion of therapy
• Daily fractions to the abdomen: Administer 8 mg orally 1-2 hours before radiotherapy; administer subsequent doses every 8 hr after first dose each day radiotherapy is given

Dosage Modifications

• Renal impairment: Dose adjustment not necessary
• Severe hepatic impairment (Child-Pugh score equal to 10): Not to exceed 8 mg/day

Cholestatic Pruritus (Off-label)

• 8 mg divided every 12 hours or 8 mg every 8-12 hours orally for 7 days up to 5 months
• Alternatively, 4-8 mg intermittent short-term intravenous dosing is used in adults; a single dose of 4 mg single dose used in pregnancy

Uremic Pruritus (Off-label)

• 8 mg divided every 12 hours or 8 mg every 8 to 12 hours orally for 14 days up to 5 months

Spinal Opioid-Induced Pruritus (Off-label)

Prophylaxis

• 4-8 mg intravenously 20-30 min before spinal opioid therapy; may repeat dosing at 12, 24, 36, 48 hours after spinal opioid dosing

Treatment

• 4-8 mg intravenously

Rosacea (Off-label)

• 4-8 mg orally every 12 hours for up to 3 weeks
• Alternatively, 12 mg IV daily for 4 days

Hyperemesis Gravidarum (Off-label)

• 10 mg IV every 8 hours as needed

Pediatric

Chemotherapy-Induced Nausea and Vomiting

Prophylaxis, Oral Dosing

• Children under 4 years old: Safety and efficacy not established
• Children 4-12 years: 4 mg started 30 min before chemotherapy, then 4 and 8 hours after the first dose, then every 8 hours for 1-2 days after chemotherapy
• Children over 12 years: 8 mg started 30 min before chemotherapy, then every 12 hours for 1-2 days after chemotherapy or single dose of 24 mg

IV Dosing

• Children under 6 months: Safety and efficacy not established
• Children 6 months or older: 0.15 mg/kg over 15 min administered 30 min before chemotherapy, then repeated 4 and 8 hours after the first dose; not to exceed 16 mg/dose (32 mg no longer recommended because of increased risk of QT prolongation)

Postoperative Nausea and Vomiting

Prophylaxis

1 month-12 years

• Under 40 kg, 0.1 mg/kg intravenously
• Over 40 kg, 4 mg intravenously

Under 12 years

• 4 mg intravenously/intramuscularly immediately before anesthesia or after the procedure or 16 mg orally 1 hour before anesthesia; patients over 80 kg may need an additional 4 mg intravenously

QUESTION

Pancreatitis is inflammation of an organ in the abdomen called the pancreas.
See Answer

Overdose

• Ondansetron overdose can increase serotonin levels and lead to serotonin syndrome.
• There is no specific antidote for ondansetron overdose.
• Overdosage must be treated with symptomatic and supportive therapy. In case of overdose, get medical help or contact Poison Control Center immediately.

What drugs interact with ondansetron?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

• Severe interactions of ondansetron include:
  • apomorphine
  • dronedarone
  • lefamulin
  • posaconazole
• Ondansetron has serious interactions with at least 147 different drugs.
• Ondansetron has moderate interactions with at least 83 different drugs.
• Ondansetron has minor interactions with at least 25 different drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

• Use of ondansetron may be acceptable. Animal studies do not show evidence of fetal harm and studies on ondansetron use during pregnancy have reported inconsistent findings on major birth defects in the newborn. Available postmarketing data do not reveal a drug-associated risk of miscarriage or adverse maternal outcomes.
• It is not known if ondansetron is present in human breast milk; however, it is present in rat’s milk, and likely also present in human milk. There is no data on its effects on milk production or the breastfed infant. Use with caution in nursing mothers, based on the mother's clinical needs and the potential adverse effects on the infant.