👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-08-23🏷️ Pharmacological Therapies🔖 Free to read, print, and share
Also known as: Zofran · anti-nausea/anti-vomiting drug · 5-HT3 blocker · the -setron drug
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Use this quick-reference guide to spot, treat, and prevent Ondansetron on the NCLEX. Keep it handy during review and on exam day!
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📒 The 1-minute cheat sheet
📌 Uses
N/V: chemo, post-op, pregnancy
Blocks serotonin → antiemetic
🩺 Signs
Headache, constipation, dizziness
🚩 Report
QT prolongation → torsades risk
Serotonin synd w/ SSRIs/triptans
🧪 Labs
Monitor K+, Mg+, baseline ECG
Give before chemo for best effect
📚 Ondansetron — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Ondansetron is a serotonin 5-HT3 receptor antagonist used to prevent and treat nausea and vomiting from chemotherapy, radiation, surgery, and pregnancy. It blocks serotonin both centrally in the chemoreceptor trigger zone and peripherally in the GI tract. Memory aid: the -setron suffix marks the 5-HT3 antiemetics.
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Key points
Understand these first
Prevents and treats nausea/vomiting by blocking 5-HT3 serotonin receptors.
Prolongs the QT interval and can cause life-threatening dysrhythmias such as torsades de pointes.
Headache and constipation are the most common side effects.
Can contribute to serotonin syndrome when combined with SSRIs, SNRIs, or other serotonergic drugs.
Available as IV, oral tablet, and orally disintegrating tablet (ODT).
Give before chemotherapy or anesthesia for prophylaxis rather than waiting for vomiting.
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Nursing priorities
What to do, in order
Obtain a baseline ECG/QT interval and electrolytes in at-risk patients.
Monitor potassium and magnesium and correct deficits to lower dysrhythmia risk.
Assess for relief of nausea/vomiting and monitor hydration status.
Handle ODT with dry hands and place on the tongue to dissolve without water.
Watch for signs of serotonin syndrome when given with other serotonergic agents.
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Red flags — report now
Escalate immediately
Report palpitations, syncope, dizziness, or an irregular heartbeat (QT prolongation/torsades).
Report agitation, fever, tremor, sweating, or hyperreflexia suggesting serotonin syndrome.
Hold and report in patients with congenital long QT syndrome or uncorrected hypokalemia/hypomagnesemia.
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Labs & values
Numbers to know
Potassium 3.5-5.0 mEq/L
Magnesium 1.3-2.1 mg/dL
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Patient teaching
What patients must know
Report fainting, chest fluttering, or a fast/irregular heartbeat right away.
Increase fluids and fiber to prevent constipation.
Tell your provider all medications, especially antidepressants.
Take antiemetic before activities or treatments that trigger nausea when possible.
❓ Ondansetron: NCLEX FAQs
What are the priority nursing interventions for Ondansetron?
Obtain a baseline ECG/QT interval and electrolytes in at-risk patients. Monitor potassium and magnesium and correct deficits to lower dysrhythmia risk. Assess for relief of nausea/vomiting and monitor hydration status. Handle ODT with dry hands and place on the tongue to dissolve without water.
What are the warning signs of Ondansetron a nurse must report?
Report palpitations, syncope, dizziness, or an irregular heartbeat (QT prolongation/torsades). Report agitation, fever, tremor, sweating, or hyperreflexia suggesting serotonin syndrome. Hold and report in patients with congenital long QT syndrome or uncorrected hypokalemia/hypomagnesemia.
What do I need to know about Ondansetron for the NCLEX?
Prevents and treats nausea/vomiting by blocking 5-HT3 serotonin receptors. Prolongs the QT interval and can cause life-threatening dysrhythmias such as torsades de pointes. Headache and constipation are the most common side effects. Can contribute to serotonin syndrome when combined with SSRIs, SNRIs, or other serotonergic drugs.
What patient teaching is important for Ondansetron?
Report fainting, chest fluttering, or a fast/irregular heartbeat right away. Increase fluids and fiber to prevent constipation. Tell your provider all medications, especially antidepressants. Take antiemetic before activities or treatments that trigger nausea when possible.
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Quick Tip
Prevents and treats nausea/vomiting by blocking 5-HT3 serotonin receptors.