Zofran pediatric dose calculator
Use this Zofran pediatric dose calculator to turn a by-weight ondansetron plan into the right 4 mg/5 mL liquid or ODT dose, then pair it with a practical oral rehydration workflow.
Zofran (ondansetron) dosage chart by weight for children (4 mg/5 mL liquid)
For one dose of ondansetron liquid for vomiting with stomach flu in children 6 months and older (8 kg or more): 0.15 mg/kg, capped at 2 mg up to 15 kg, 4 mg up to 30 kg and 8 mg above. Use the dose your child's prescriber ordered.
- Many prescribers use a fixed dose instead: 2 mg (2.5 mL) for 8-15 kg, 4 mg (5 mL) for 15-30 kg, 8 mg (10 mL) over 30 kg. That is also standard and may be more than this chart. Give the mL on your pharmacy label; if it matches neither, call the pharmacist. Don't change the dose yourself.
- This chart is one dose. Repeat doses only if prescribed: at least 8 hours apart, no more than 3 doses in 24 hours, for up to 2 days (DOSE-AGE).
- Only for 4 mg/5 mL liquid. Dissolving tablets (ODT 4 mg and 8 mg) are dosed by weight band, not mL: ask the prescriber.
| Weight (kg) | Weight (lb) | One dose: 0.15 mg/kg (weight-band maximum)mL of 4 mg/5 mL oral solution per dose (mg it contains) |
|---|---|---|
| 8check age: 6 months and older | 18 | 1.5 mL (1.2 mg) |
| 10 | 22 | 1.9 mL (1.5 mg) |
| 12 | 26 | 2.3 mL (1.8 mg) |
| 15 | 33 | 2.5 mL (2 mg) max dose |
| 18 | 40 | 3.4 mL (2.7 mg) |
| 20 | 44 | 3.8 mL (3 mg) |
| 25 | 55 | 4.7 mL (3.8 mg) |
| 30 | 66 | 5 mL (4 mg) max dose |
| 35 | 77 | 6.5 mL (5.2 mg) |
| 40 | 88 | 7.5 mL (6 mg) |
- 0.15 mg/kg as one dose (the home oral-solution dose in the DOSE-AGE trial, NEJM 2025), no more than the Freedman 2006 band doses: 2 mg up to 15 kg, 4 mg up to 30 kg, 8 mg above. Off-label use for stomach flu.
- Fixed band doses come from emergency department trials of dissolving tablets (Freedman 2006; some protocols use 6-8 mg over 30 kg). A 2 mg dose is half a 4 mg tablet.
- Under 6 months or under 8 kg: ask the prescriber.
- Avoid with long QT syndrome; tell the prescriber about other medicines that affect heart rhythm (label). Call a doctor for signs of dehydration, green (bile) or bloody vomit, blood in stool, severe belly pain, or a very sleepy child.
- mL is rounded to 0.1 mL under 5 mL and to 0.5 mL from 5 mL (AAP metric dosing), never above the maximum; use an oral syringe.
Printable
Printable dosing sheet
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Zofran liquid or ODT dose
Ondansetron and Zofran dose calculator details for vomiting plans
Ondansetron searches usually need a fast Zofran liquid or ODT dose plus a reminder that medication is only one part of an oral rehydration plan.
Formula
mL per dose = prescribed ondansetron mg per dose / (4 mg / 5 mL), which equals prescribed mg per dose / 0.8 mg per mL.
Worked example
If the plan is 4 mg ondansetron and the bottle is 4 mg/5 mL, the measured volume is 5 mL; if using ODT, match the tablet strength instead.
Safety checks before using the result
- Escalate persistent vomiting, blood or bile, lethargy, or signs of dehydration.
- Confirm the product form before converting mg into mL.
- Review QT-risk cautions when there is a cardiac history or interacting medication list.
Specific dosing support
Common formulation searches for Ondansetron
Practical dosing guide
Before you measure the dose
Use this page when the goal is a clear ondansetron dose tied to oral rehydration, the form the child can keep down, and the safety checks that matter before redosing.
- 4 mg/5 mL liquid
- The common ondansetron liquid is 4 mg/5 mL, so the main job is converting the mg/kg target into the right mL and matching it to the exact bottle in hand.
- 4 mg or 8 mg ODT
- ODT is often easier than liquid during active vomiting because it avoids measuring a spoonful or syringe dose.
- Single-dose rehydration plan
- A common outpatient workflow uses one ondansetron dose, then restarts small sips of oral rehydration solution after the medicine has had time to work.
Ondansetron pediatric medication summary
Ondansetron (Zofran) helps control nausea and vomiting in children. Use this page to calculate a pediatric Zofran dose, choose the matching liquid or ODT option, and pair the dose with a practical oral rehydration plan.
Common pediatric use: reduce vomiting so oral rehydration is possible
Onset ~30–60 minutes; effect often allows small sips of fluids
Ondansetron indications and common pediatric uses
Ondansetron is a selective 5-HT3 antagonist used to control nausea and vomiting from gastroenteritis, chemotherapy, and perioperative settings. Its goal in acute gastroenteritis is to enable oral rehydration, not eliminate all vomiting.
Acute gastroenteritis with vomiting preventing oral rehydration
Acute gastroenteritis with vomiting preventing oral rehydration: Take-home doses, if prescribed, should follow a written plan (at least 8 hours apart, max 3 doses in 24 hours, up to 48 hours, per the 2025 DOSE-AGE trial); reassess for surgical abdomen or metabolic etiologies if vomiting persists after 2 doses.
Chemotherapy-induced nausea and vomiting (CINV)
Chemotherapy-induced nausea and vomiting (CINV): Combine with dexamethasone ± NK1 antagonists for highly emetogenic regimens; monitor QTc with high doses.
Postoperative nausea and vomiting (PONV) prophylaxis
Postoperative nausea and vomiting (PONV) prophylaxis: Combine with dexamethasone or droperidol for high-risk patients.
Cyclic vomiting syndrome abortive therapy
Cyclic vomiting syndrome abortive therapy: Administer at prodrome with hydration and anti-migraine regimen; coordinate with gastroenterology.
How to give Ondansetron
- Practical pediatric administration guidance for ondansetron across home, urgent care, and discharge settings.
- Shake liquid formulations, measure with an oral syringe, and administer slowly toward the inner cheek. For ODT, peel foil with dry hands and let tablet dissolve fully on tongue. Start oral rehydration 10-20 minutes after dosing if nausea improves.
Ondansetron side effects, contraindications, and interactions
Ondansetron is usually well tolerated, but side-effect safety depends on dosing discipline and rapid recognition of rare cardiac or allergic events.
Common side effects
- Support common mild effects with hydration and short-interval follow-up.
- Avoid unsupervised repeat dosing for persistent vomiting.
- Escalate immediately for fainting, palpitations, severe abdominal pain, or allergic swelling.
Safety checks
- Congenital long-QT syndrome: Ondansetron can prolong QT and trigger arrhythmias.
- Electrolyte disturbances (hypokalemia, hypomagnesemia): Electrolyte abnormalities increase QT risk.
- Syncope, palpitations, or chest pain after dosing: Possible arrhythmia or QT prolongation.
- Agitation, hyperreflexia, clonus with serotonergic stacks: Possible serotonin toxicity.
Drug interactions
- Review the full medication list with a clinician or pharmacist before combining therapies.
Ondansetron mechanism and clinical pearls
Ondansetron reduces nausea and vomiting by blocking serotonin 5-HT3 receptors on peripheral vagal afferents and central emetic pathways. This mechanism creates a short symptom-control window that helps children rehydrate, but it does not treat the underlying infection or surgical pathology. Mechanism-linked safety limits include QT-risk amplification at higher exposure or with interacting medications.
Have oral rehydration supplies ready and begin small frequent sips as soon as nausea improves. Medication benefit is highest when this hydration window is used immediately.
Before repeat or IV use, screen for congenital long QT, syncope history, electrolyte depletion, and QT-prolonging co-medications.
For uncomplicated viral gastroenteritis, one weight-based dose is usually sufficient to support oral rehydration.
In chemotherapy pathways, combine ondansetron within protocol-defined multi-agent antiemetic regimens and predefine rescue options.
Frequently asked questions about Ondansetron
Yes. Zofran is a brand name for ondansetron. The calculator works from the active ingredient and then helps you match the result to a liquid or ODT strength.
A common outpatient dose is 0.15 mg/kg. The calculator converts that mg/kg target into mL of the 4 mg/5 mL liquid (max 8 mg). It does not pick an ODT strength; ODT tablets (4 mg, 8 mg) are chosen by the prescriber by weight band.
ODT is often easier during active vomiting because it avoids measuring and swallowing a full spoonful. Liquid works well when the child can reliably keep down a measured oral dose and the caregiver wants the exact mL conversion.
The calculator converts the weight-based mg target into mL using the common 4 mg/5 mL concentration. That is usually the fastest way to move from the bottle in hand to the exact dose.
If vomiting happens immediately after the dose, call your clinician for guidance before repeating it. If some time has passed and your child is improving, shift the focus to small, frequent sips of oral rehydration solution.
Ondansetron usually starts helping within 30–60 minutes, which often allows children to keep down small sips of fluids and begin rehydrating.
Yes. It can be given with a small sip of water, and once nausea eases, start frequent small sips of oral rehydration solution. This is a common and expected approach.
Ondansetron can interact with medicines that affect heart rhythm (QT prolongation) or with apomorphine. Share all medications with your clinician to ensure safe use.
Ondansetron is not a sedating medicine. Some children feel tired while recovering from illness, which is common and usually improves as hydration and comfort improve.
Yes—these do not typically interact. If your child has stomach pain or fever, acetaminophen is often preferred; always follow dosing guidance and consult your clinician if unsure.
Sources reviewed for Ondansetron
https://publications.aap.org/pediatrics/article/127/3/e587/30339
https://www.acep.org/pediatrics/education/education-articles/ondansetron-for-the-treatment-of-gastroenteritis.shtml
https://pubmed.ncbi.nlm.nih.gov/40673584/
Ondansetron – Medicines for Children
MfC
SourceOndansetron – NHS
NHS
SourceOndansetron – MedlinePlus
MedlinePlus
Source