Focus on Pharmacology: Ondansetron
Ondansetron (brand name Zofran) is a very common medication you’ll see in the clinical setting, on your care plans, and sprinkled throughout nursing school exams. Let’s go through ondansetron using the Straight A Nursing DRRUGS framework.
D: Drug Class
Ondansetron (brand name Zofran) is a great example of a medication you’ll be more likely to recognize by therapeutic class than by pharmacologic class. However, understanding the pharmacologic class helps you further understand how and why it works.
Ondasetron’s therapeutic class is antiemetic, and it’s pharmacologic class is five HT3 antagonist. Now, you’re probably asking, “What is five HT3?” (because that’s exactly what I said when I first saw it!. Five HT is an abbreviation for serotonin, which can be written out by its full name 5-hydroxytryptamine (but who has time for that, right?). As a serotonin antagonist, ondansetron is going to block the serotonin receptor (thereby blocking the effects of serotonin). It does this in two places…on vagal nerves in the GI tract and on chemoreceptors in the brain. The result is that ondansetron has powerful antiemetic effects.
Ondansetron can be by mouth as a dissolvable tablet, a dissolvable film, a tablet, or a liquid solution. It can also be administered intramuscularly or intravenously, which is how it is given most often in the in-patient setting. The dissolvable tablets are used more in outpatient or at home.
R: Regular Dose Range
For adults and children older than 11, the general PO dose is 4 or 8mg, though much higher doses may be used to prevent nausea/vomiting with certain types of chemotherapy (up to 24mg).
The IV/IM dose for adults is generally 4mg, though you could see weight-based doses for adults at 0.15mg/kg with a maximum dose of 16mg. IV doses for kids range from 0.1mg/kg to 0.15mg/kg.
However, the most common dose you’ll see is 4mg PO and IV.
It’s important to note that in hepatic impairment, your ondansetron dose is not to exceed 8mg/day.
Ondansetron is given to prevent or stop nausea/vomiting in a variety of situations:
- Before and after chemotherapy
- During and after surgery. Anesthesia causes nausea, so the anesthesiologist will often give ondansetron right before they reverse the anesthetic to prevent postoperative nausea/vomiting.
- To prevent nausea/vomiting in hyperemesis gravidarum, a complication of pregnancy that involves persistent vomiting.
Ondansetron administration is relatively straightforward, and is most effective if given before chemotherapy or anesthesia.
- IV push ondansetron should be given over at least 30 seconds, but slower is preferred (2-5 minutes)
- Teach the patient to notify you or their physician (if outpatient) if they notice involuntary movements of the limbs, face or eyes, an irregular heartbeat or show signs of serotonin syndrome (see below).
- Be careful to only touch the disintegrating tablet with dry hands, otherwise it will start to dissolve before you can give it to the patient!
- Make sure the patient understands not to swallow disintegrating tablets or films. They will dissolve and be swallowed with saliva.
- Some ondansetron tablets are not the dissolving type, so make sure you know which type you are using (most are dissolving, though!).
- Don’t try to push the dissolvable ondansetron through the blister pack. The tablets are fragile and this could damage it. Simply peel the backing off the blister pack and then remove the dissolvable tablet.
S: Side effects
The most common side effects of ondansetron are headache, fatigue, constipation and diarrhea. The most SERIOUS and life-threatening side effects are:
- Serotonin syndrome (especially with the use of other serotonergic drugs such as SSRIs, SNRIs, MAOIs, fentanyl, lithium, tramadol and methylene blue.)
- Torsade de pointes (check that QT interval!)
- Stevens-Johnson syndrome
- Toxic epidermal necrolysis (TENS).
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Brodhead, P. (2015, April 13). Zofran and serotonin syndrome. Spangenberg Shibley & Liber LLP. https://www.spanglaw.com/blog/2015/april/zofran-and-serotonin-syndrome/
Davis’s Drug Guide. (n.d.). Ondansetron (Zofran, zuplenz) | davis’s drug guide. Davis’s Drug Guide. Retrieved June 24, 2021, from https://www.drugguide.com/ddo/view/Davis-Drug-Guide/51560/all/ondansetron?refer=true
Theriot, J., Wermuth, H. R., & Ashurst, J. V. (2021). Antiemetic serotonin-5-ht3 receptor blockers. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK513318/