Ondansetron
Ondansetron hydrochloride
Brand names:Zofran, Zofran ODT, Zuplenz
A selective 5-HT3 serotonin receptor antagonist and the standard antiemetic across TCCC, TECC, and civilian EMS protocols. Ondansetron is the first-line agent for post-trauma, post-opioid, and chemotherapy-induced nausea due to its excellent efficacy, minimal sedation, and clean operational profile. The ODT (orally disintegrating tablet) form is particularly useful in field settings where water access is limited.
Pharmacology and Actions
Ondansetron selectively antagonizes 5-HT3 serotonin receptors located peripherally on vagal afferent nerves and centrally in the chemoreceptor trigger zone (CTZ) of the area postrema. Serotonin release from enterochromaffin cells triggers nausea and vomiting via these receptors; blocking them prevents the cascade. The selectivity for 5-HT3 (rather than dopaminergic or histaminic receptors) is responsible for the clean side effect profile compared with metoclopramide or promethazine.
Indications
- Trauma-associated nausea and vomiting
- Opioid-induced nausea and vomiting
- Chemotherapy-induced nausea and vomiting
- Postoperative nausea and vomiting (PONV)
- Hyperemesis gravidarum (off-label, but commonly used)
- TCCC analgesia adjunct - administered routinely with opioid analgesia in tactical care
Absolute Contraindications
- Known hypersensitivity to ondansetron or other 5-HT3 antagonists
- Concurrent apomorphine use (severe hypotension)
- Congenital long QT syndrome
Precautions and Side Effects
Common: headache (most common, 10 to 15 percent), constipation, fatigue, malaise. Cardiac: QT prolongation, particularly with IV doses above 16 mg single dose (FDA reduced max IV single dose to 16 mg in 2012). Risk increases with hypokalemia, hypomagnesemia, congenital long QT, and concurrent QT-prolonging medications. Serotonin syndrome possible when combined with other serotonergic agents (SSRIs, SNRIs, MAOIs, tramadol, fentanyl). Rare: hypersensitivity reactions including anaphylaxis. Drug interactions: additive QT prolongation with amiodarone, sotalol, methadone, haloperidol; serotonin syndrome risk with serotonergic agents; apomorphine contraindicated. Half-life 3 to 6 hours. Pregnancy Category B (extensively used in pregnancy; recent data suggest small but possibly increased cleft palate risk in first trimester - balance against severity of hyperemesis). Compatible with lactation. Pediatric dosing well established. Renal impairment: dose adjust if severe. Hepatic impairment: reduce dose. Monitor QT interval and electrolytes in at-risk patients.
Adult Dosing
Pediatric Dosing
Children 6 months and older: 0.15 mg/kg IV/IM/PO every 8 hours (max 4 mg per dose under 40 kg, 8 mg per dose over 40 kg). PO: 4 mg if 4 to 11 years; 8 mg if 12 years and older.
Pharmacokinetics
Peak Effect: IV: 15 to 30 minutes. PO/ODT: 1 to 2 hours.
Duration: 4 to 8 hours.
Storage and Handling
Store at room temperature (15 to 30 degrees C). Protect from light. ODT formulation in foil-sealed blister packs is stable in standard IFAK and aid bag conditions. IV vials and ampules stable at room temperature.
Reconstitution:
IV solution typically supplied at 2 mg/mL. For IV bolus: dilute in 50 mL D5W, NS, or LR and infuse over 15 minutes for chemotherapy doses; rapid push acceptable for 4 mg dose in trauma settings. ODT requires no reconstitution - peel foil, place on tongue, allow to dissolve.
TCCC and TECC Role
Ondansetron is the TCCC and TECC standard antiemetic. TCCC 2026 Guidelines recommend ondansetron 4 mg ODT every 8 hours as needed for casualties with nausea, and it is administered prophylactically with opioid analgesia (fentanyl, morphine) to prevent opioid-induced nausea and vomiting. The ODT form is doctrine for the tactical field care window - no IV access required, no water required, rapid dissolution on tongue, reliable absorption. Mission impact is none at standard doses, making it the cleanest operational antiemetic available.
Ondansetron is one of the most important medications in tactical and operational EMS. The 4 mg ODT format is purpose-built for field use: pull from the IFAK, place on tongue, dissolves in 30 seconds, works within 30 to 60 minutes. Standard TCCC practice is to administer ondansetron 4 mg ODT routinely with opioid analgesia - waiting for nausea to develop is poor management when prevention is this clean. For the rare patient who does not respond to ondansetron, consider metoclopramide (with the operational tradeoffs) or promethazine. The TCCC standard dose is 4 mg, not 8 mg; the lower dose has equivalent efficacy with lower QT risk.
Treating ondansetron as a reactive medication. The TCCC protocol pairs it with opioid administration prophylactically - giving fentanyl OTFC without simultaneously giving ondansetron ODT is suboptimal practice that predictably produces preventable vomiting in a casualty being moved through evac. The other mistake is single doses above 16 mg IV - the QT prolongation risk rises sharply above this ceiling. Repeat 4 to 8 mg doses every 8 hours rather than escalating single-dose magnitude.
This drug profile is provided as educational reference material for trained medical providers. It is not medical advice, not a substitute for formal training, and not a substitute for current published guidelines or medical direction.
Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances are subject to additional handling, accountability, and documentation requirements per DEA and state law. Always verify dosing, indications, contraindications, and route of administration against current published guidelines and your local protocols before administration.
If this content is being viewed during a medical emergency, call 911 immediately and follow the direction of your local emergency dispatch and medical control. Do not use this reference as a substitute for emergency medical services.
Drug information evolves. Last reviewed dates and source citations are provided for each entry. Confirm currency against the cited source before clinical use.
Penn Tactical Solutions publishes this reference for educational purposes. PTS does not provide medical direction and does not assume responsibility for clinical decisions made in the field. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Educational reference for trained medical providers. Not medical advice. Not a substitute for formal training, current published guidelines, or medical direction. Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances require additional storage, accountability, and documentation per DEA and state law.
In a medical emergency, call 911. This reference is not a substitute for emergency medical services.
Verify dosing, indications, and contraindications against current published guidelines and your local protocols before administration. Confirm content currency against the source citation. Penn Tactical Solutions does not provide medical direction. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Ondansetron
| IV/IO | 4 mg IV over 2 to 5 minutes every 8 hours as needed. Maximum 16 mg as a single IV dose. For chemotherapy: 8 mg IV 30 minutes before chemo, then 8 mg every 8 hours. (Within 30 minutes) |
| IM | 4 mg IM every 8 hours as needed. Useful when IV access not available; absorption is reliable. (Within 30 minutes) |
| IN | None (None) |
| PO | 4 to 8 mg PO every 8 hours as needed for nausea. ODT (orally disintegrating tablet) 4 or 8 mg placed on tongue, dissolves in 30 seconds, no water needed - the operational form of choice. (30 to 60 minutes (ODT: similar)) |