How the dose is calculated
Ondansetron is dosed as a single mg/kg amount per administration, capped at a maximum, rather than a total daily dose — select the indication for the correct per-kg dose, cap, and repeat interval.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Nausea/vomiting | 0.15 mg/kg | every 8h as needed | 8 mg per dose |
| Post-op nausea/vomiting | 0.1 mg/kg | single dose | 4 mg per dose |
Clinical use
- Ondansetron is widely used for gastroenteritis-related vomiting, post-operative nausea and vomiting, and chemotherapy-induced nausea, with oral and IV forms considered similarly effective for mild-moderate symptoms.
- A single oral dose for acute gastroenteritis can reduce vomiting enough to allow oral rehydration, potentially avoiding IV fluids and admission in appropriate patients.
- Can prolong the QT interval — use caution with other QT-prolonging drugs, electrolyte disturbances (especially hypokalaemia/hypomagnesaemia), or known arrhythmia risk.
- Headache and constipation are the most common side effects; serotonin syndrome is a rare risk when combined with other serotonergic drugs (e.g. SSRIs).
Frequently asked questions
What is ondansetron used for?
Ondansetron is an antiemetic used for nausea and vomiting from gastroenteritis, post-operative recovery, and chemotherapy, among other causes.
Can ondansetron help avoid IV fluids for a vomiting child?
Yes — a single oral dose can reduce vomiting enough to allow oral rehydration therapy to succeed in many children with gastroenteritis, potentially avoiding the need for IV fluids or hospital admission.
Does ondansetron affect heart rhythm?
It can prolong the QT interval, so it's used cautiously in patients with existing QT prolongation, significant electrolyte disturbances, or on other QT-prolonging medications.
How often can ondansetron be repeated?
For general nausea/vomiting, doses are typically spaced at least 8 hours apart with a maximum of 3 doses in 24 hours — follow the specific product/protocol guidance for the indication being treated.
References
- American Academy of Pediatrics. Clinical Practice Guideline — Management of Acute Gastroenteritis.
- British National Formulary for Children (BNFc) — Ondansetron.
- Gan TJ, et al. Consensus Guidelines for the Management of Postoperative Nausea and Vomiting. Anesth Analg. 2020.