Ondansetron Pediatric Dose Calculator
Calculate ondansetron (Zofran) doses for children by weight for gastroenteritis vomiting, post-operative nausea, and chemotherapy-induced nausea.
Ondansetron Pediatric Dose Calculator
Evidence-based weight-adjusted dosing
How to Use This Calculator
Enter Weight
Input the child's weight in kilograms.
Select Indication
Choose the clinical scenario — gastroenteritis, post-op, or chemo-induced.
Choose Formulation
Select ODT tablet or oral solution.
Review Dosing
Check the per-dose amount and clinical guidance notes.
How We Calculate
Ondansetron is a 5-HT3 receptor antagonist widely used in pediatric emergency settings for acute gastroenteritis vomiting. The AAP recommends 0.15 mg/kg as a single oral dose (max 4 mg for <40 kg, max 8 mg for ≥40 kg) for children 6 months and older with vomiting from acute gastroenteritis who are at risk for dehydration. For post-operative nausea, 0.1 mg/kg (max 4 mg) is the standard dose.
The orally disintegrating tablet (ODT) is particularly useful for vomiting children as it dissolves on the tongue without water and can be absorbed even if the child vomits shortly after administration. The oral solution (4 mg/5 mL) allows precise weight-based dosing for younger children.
Ondansetron carries a small risk of QT prolongation. It should be used cautiously in patients with congenital long QT syndrome, electrolyte abnormalities, or concurrent use of other QT-prolonging medications. A single dose for gastroenteritis carries minimal cardiac risk. This tool is for educational reference only.
Sources & References
- AAP Clinical Practice Guideline — Acute Gastroenteritis in Children (aap.org)
- Lexicomp Pediatric Drug Information — Ondansetron (wolterskluwer.com)
- FDA Prescribing Information — Ondansetron (Zofran) (fda.gov)
Data last verified:
Frequently Asked Questions
The ondansetron ODT is placed on the tongue where it dissolves in seconds without needing water. The dissolved medication is swallowed with saliva and absorbed in the GI tract. This formulation is ideal for vomiting children because it can be administered even when the child is actively nauseated. If the child vomits within a few minutes, most of the drug has already been absorbed from the dissolved tablet.
Ondansetron is recommended for children 6 months and older with acute gastroenteritis vomiting. Below 6 months, the safety data is limited and the risk-benefit profile is less clear. For infants under 6 months with vomiting, the priority is frequent small-volume oral rehydration and close monitoring for dehydration. The prescriber should determine appropriateness for any child under 1 year.
Ondansetron can cause dose-dependent QT interval prolongation. The risk is highest with IV administration and higher doses used in chemotherapy. A single oral dose for gastroenteritis carries minimal cardiac risk in otherwise healthy children. However, it should be avoided or used with caution in children with known congenital long QT syndrome, hypokalemia, hypomagnesemia, or those taking other QT-prolonging medications.
For acute gastroenteritis, a single dose is the standard recommendation per AAP guidelines. The goal is to stop vomiting long enough to allow successful oral rehydration. A second dose may be given if vomiting recurs, but routine multi-dose therapy for gastroenteritis is not recommended. For chemotherapy-induced nausea, scheduled multiple doses every 8 hours are used per oncology protocols.
Ondansetron effectively suppresses vomiting regardless of the cause, which means it can potentially mask symptoms of more serious conditions such as appendicitis, bowel obstruction, or increased intracranial pressure. Before administering ondansetron, a proper clinical evaluation should be performed to rule out surgical or life-threatening causes of vomiting. In emergency settings, physicians assess for red flags before prescribing.
Constipation is the most common side effect of ondansetron, occurring because the drug blocks serotonin receptors in the gut that stimulate motility. Headache is the second most common side effect. Both are typically mild and self-limiting. For a single dose used in gastroenteritis, side effects are minimal. With repeated dosing for chemotherapy, constipation may require management with stool softeners or increased fluid intake.
Ondansetron has relatively few significant drug interactions. The most important interaction is with other QT-prolonging medications, which can increase the risk of cardiac arrhythmias. Apomorphine is contraindicated with ondansetron due to risk of profound hypotension. Serotonergic medications (SSRIs, SNRIs) can theoretically increase the risk of serotonin syndrome when combined with ondansetron, though this is rare at standard doses.
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