Ondansetron (Zofran)

Ondansetron (Zofran)


February 23, 2024

Welcome to UH EMS-I’s Pharmacy Phriday. A common complaint EMS may encounter in the pre-hospital setting, as well as a side effect to some of the medications administered by our personnel, is the complaint of nausea and vomiting (n/v). In this week’s installment, we will review the recommended medication to address such a concern or complaint.

Ondansetron is the preferred antiemetic in our protocols that can be found within the “Nausea/Vomiting” protocol, as well as various other locations in the protocols where nausea and vomiting are of concern. The medication is a rapid-acting serotonin receptor antagonist, which essentially means it blocks the vomiting impulse from being sent to the brain and thus suppresses nausea and vomiting. 

There are obviously numerous causes of nausea and vomiting that the provider must explore, but whatever the cause, it is an unpleasant experience for the patient as well as the provider. In addition, nausea and vomiting can lead to very serious illnesses or complications. Some of these may include dehydration and electrolyte imbalances, aspiration, or other airway compromises. Nausea and vomiting can worsen a hemorrhagic stroke or cause intracranial hemorrhage that is controlled to start bleeding again. UH protocols also recognize the importance of early treatment of nausea and preventing vomiting. 


Ondansetron is provided and approved for administration by paramedics in the IV/IM form as a 4mg/2ml vial. It is also provided in the ODT (Oral Dissolving Tablet) form, which can also be administered by AEMTs. Adult dosing is 4 mg initially, which can be repeated in 10 minutes if needed, to a maximum dose of 8 mg. 

In the pediatric patient over the age of 1, the dosing of the IV/IM solution is 0.15 mg/kg to a maximum dose of 4 mg. This solution can also be administered PO by drawing up the medication, removing the needle, and using the syringe to “shoot” it past their tongue. The ODT form can only be used in the pediatric patient if they are over 40 kg in weight and at least 12 years of age. Doses of Ondansetron are not repeated in the pediatric patient.


Contraindications for the use of Ondansetron include a known allergy, liver disease (the medication is metabolized in the liver), or the presence of a prolonged QT interval of greater than 500 ms or 2.5 large boxes if noted on an ECG. 


Precautions listed within the protocol for the use of Ondansetron include pregnancy and a history of prolonged QT conditions or concerns. The QT prolongation is a very rare side effect of the medication that can lead to Torsades de Pointes or other lethal arrhythmias. This side effect is more of a concern in the following patients and circumstances:

One of the most common side effects associated with Ondansetron includes a headache. A slow IV push over 2 minutes will help reduce the risk of this and other side effects. Other side effects listed include GI changes, fatigue, and general weakness.


Additional considerations when administering Ondansetron to your patient may include: 

The use of Ondansetron in the pre-hospital setting, when used within guidelines, is yet another example of how we in EMS can have a positive effect on the outcome of a patient’s experience with emergency health care. Your caring and compassionate attitude for your patients makes a difference. Keep up the great work and stay safe!


The UH EMS-I Team

University Hospitals

January 13, 2023

Dear Colleagues,

Good day!  Welcome back to the weekly Pharmacy Phriday CE offering.  You are encouraged to also check out UH EMS I’s Monday Morning Medical Director’s weekly offering.  This past week’s article (January 9, 2023) provided a review of Push Dose Epi and the recent protocol changes related to that medication.  In today’s offering, we will continue to review protocol changes affecting medications in our UH drug boxes by looking at Zofran.


Last week’s Pharmacy Phriday mentioned Zofran as a medication frequently administered in the prehospital setting.  It is a common anti-emetic approved for use by the UH provider to treat or prevent nausea and vomiting in our patients.  As well as being provided an IV solution, an oral disintegrating tablet (ODT) form is also provided for ease of administration as well as use by the Advanced EMT. 

Adult dosing of IV/IM Zofran under the UH protocol is 4 mg, repeated in 10 minutes if needed, to a maximum dose of 8 mg.  In the pediatric patient > 1 year old, the dosing of the IV/IM solution is 0.15 mg/kg, to a maximum dose of 4 mg, that can be administered PO in the child >1 year of age if needed. The ODT dosing is a 4 mg tablet and can be administered to the adult or pediatric patient if they are over 40 kg in weight and at least 12 years of age.


The dosing in the 2023 protocol did not change.  Changes that did occur include the removal of repeat doses for the pediatric patient as well as a clarification regarding the administration of the medication for a patient who has a prolonged QT interval.  In the past protocol, the warning read, “Do not administer if QT >500 ms (2.5 large EKG boxes)”.  In the updated version, the warning reads, “Do not administer if EKG obtained and QT >500 ms (2.5 large EKG boxes)”.  The change was made to clarify the appearance of an absolute requirement for an EKG before administering the anti-emetic.  The intent of the warning is to only hold the medication if an EKG is clinically necessary and has already been done with evidence of a long QT present.  The QT prolongation is a very rare side effect of the medication, documented as <1% in one resource, but still a concern.

The concern addressed in this warning reflected a 2012 safety warning issued by the FDA, which stated that the administration of IV Zofran could possibly increase the QT interval to the point that a dysrhythmia, primarily Torsades de Pointes, might occur.  Studies have shown that the medication can indeed prolong the QT interval, but is more of a concern in the following patients and circumstances:

With most of the above-mentioned, the provider should consider ECG monitoring as part of the assessment and treatment.  In the other cases, a good SAMPLE history would reveal concerns that would warrant an ECG before the administration of Zofran. 

The one concern that may be less familiar is LQTS.  Long QT Syndrome is an inherited genetic disorder that causes an electrical disruption of the heart’s conduction system.  It can cause potentially lethal arrhythmias leading to sudden cardiac death. It, unfortunately, is often undiscovered in many children.  The only indication may be a family history.  In these cases, as well as cases when LQTS has been diagnosed previously, it is prudent to get a 12 lead before administering Zofran. 

In addition to the prolonged QT interval, a known allergy to Zofran and underlying liver disease (the medication is metabolized in the liver) are contraindications to the use of the medication.


Look for next week’s edition of Pharmacy Phriday as we continue to review recent protocol changes.  Until then, stay safe!


The UH EMS-I Team

University Hospitals