What is Zofran®?

What Is Zofran?

What is Zofran?

Ondansetron hydrochloride, marketed as Zofran, is a prescription antiemetic drug used to treat nausea and vomiting in cancer patients undergoing chemotherapy or radiation and for the prevention of post-operative nausea and/or vomiting. The drug was developed and marketed by GlaxoSmithKline. It was first approved by the U.S. Food and Drug Administration (FDA) in January 1991 and held its patent until December 2006. At that time the first generic versions were approved by the FDA. Generic ondansetron is available in many countries under different brand names.

What is Zofran Used For?

Zofran® Details

Pharmaceutical: Zofran
Manufacturer: GlaxoSmithKline
Generic name: Ondansetron hydrochloride
Drug class: Serotonin-3 receptor antagonist (5-HT3 receptor antagonist)
CAS number: 103639-04-9


Zofran, known generically as ondansetron hydrochloride, is a selective serotonin-3 (or 5-HT3) receptor antagonist. Drugs classified as antagonists block or inhibit the action of a chemical in the body. A receptor antagonist accomplishes this by preventing the chemical (e.g., a hormone or neurotransmitter) from binding to a receptor (a site on the surface of a cell) and triggering a signal. Ondansetron suppresses vomiting and nausea by inhibiting serotonin from binding to 5-HT3 receptors. Zofran is available as a tablet, oral solution, or intravenous injection. Ondansetron HCl 4 mg tablets or ondansetron HCl 8 mg tablets are commonly prescribed.


The use of ondansetron with apomorphine is contraindicated based on reports of profound hypotension and loss of consciousness when apomorphine was administered with ondansetron. Zofran injection is contraindicated for patients known to have hypersensitivity to the drug.

Common Adverse Outcomes

  • Blurred vision
  • Constipation
  • Dizziness
  • Drowsiness
  • Headache
  • Lightheadedness
  • Muscle spasm
  • Rash
  • Tiredness

What is Zofran Serotonin Syndrome?

Serious Adverse Outcome

The FDA has issued a warning that the development of serotonin syndrome has been reported with Zofran and drugs in its class (5-HT3 receptor antagonists). Most reports have been associated with the combined use of 5-HT3 receptor antagonists with antidepressants, including both selective serotonin reuptake inhibitors (SSRIs: Prozac, Paxil, Zoloft, Celexa, Lexapro) and serotonin and norepinephrine reuptake inhibitors (SNRIs: Effexor, Cymbalta, Pristiq). Serotonin syndrome can be fatal. Symptoms may include:

  • Mental status changes
    • Agitation
    • Coma
    • hallucinations
  • Autonomic instability status changes
    • blood pressure changes
    • hyperthermia (high temperature)
    • tachycardia (fast heart rate)
  • Gastrointestinal symptoms
    • diarrhea
    • nausea
    • vomiting
  • Neuromuscular aberrations
    • hyperreflexia (overactive bodily reflexes)
    • incoordination


Ondansetron may increase the risk of developing abnormal changes in the electrical activity of the heart, which can result in a potentially fatal abnormal heart rhythm. Changes in the electrical activity of the heart (prolongation of the QT interval of the electrocardiogram) can lead to an abnormal and potentially fatal heart rhythm (including Torsade de Pointes). Patients with a particular risk for developing Torsade include those with underlying heart conditions, such as congenital long QT syndrome, those who are predisposed to low levels of potassium and magnesium in the blood, and those taking other medications that lead to QT prolongation.

Medical Studies

  • Bengt Daniellson et al., “Use of ondansetron during pregnancy and congenital malformations in the infant,” Reproductive Toxicology (50), December 2014.
  • Jon T. Andersen et al., “Ondansetron Use In Early Pregnancy And The Risk Of Congenital Malformations – A Register Based Nationwide Cohort Study,” paper presented at the International Society of Pharmacoepidemiology, Montreal, Canada, August 2013.
  • Marlene Anderka et al., “Medications Used to Treat Nausea and Vomiting of Pregnancy and the Risk of Selected Birth Defects,” Birth Defects Research (Part A) 94: 22-30 (2012).
  • Shing-Shun N. Siu et al., “Placental Transfer of Ondansetron During Early Human Pregnancy,” Clinical Pharmacokinetics 45 (4): 419-423.

Pregnancy Category

Ondansetron currently carries a Pregnancy Category B classification. Category B signifies that animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate or well-controlled studies in pregnant women, or animal studies that have shown an adverse effect, but adequate and well-controlled studies in pregnant women have failed to demonstrate a risk to the fetus in any trimester. However, the FDA recently adopted new rules replacing the letter category system, which was viewed as giving an “over-simplified view of the product risk.”

Drug labels will now be required to provide more detailed information about the risks of using a drug during pregnancy. Several recent studies have linked Zofran use during the first trimester to a variety of birth defects. A growing number of lawsuits alleging birth defects caused by Zofran are being filed.