ondansetron (zofran™)

presentation - what the drug is sealed in, its concentration and how it might look

Ondansetron can come in many presentations such as SL strips, PO tablets and other concentrations in vials or ampoules however the two listed below are the most common in ambulance practice.

  • Ampoule containing 4 milligrams of ondansetron (as hydrochloride) in 2 ml.

  • Ampoule containing 8 milligrams of ondansetron (as hydrochloride) in 4 ml.

NB: Both these preparations share the same concentration - 2 milligrams in 1 ml.

INDICATIONS - reasons you should administer this drug

  • Prevention and treatment of opiate-induced nausea and vomiting (e.g. morphine sulphate).

  • Treatment of nausea or vomiting (including travel sickness).

CONTRAINDICATIONS - reasons you should not administer this drug

  • Known sensitivity to ondansetron.

  • Infants <1 month old (as their liver is not yet mature enough to metabolise ondansetron).

  • Congenital long QT syndrome (ondansetron can prolong the QT interval further causing arrythmias).

cautions - reasons that if you administer this drug you must monitor for side effects more than usual

  • QT interval prolongation (avoid concomitant administration of drugs that prolong QT interval).

  • Hepatic impairment (see pharmacological action section).

  • Pregnancy (see pharmacological action section).

pharmacological action - what does it to the body and what does the body do to it?

FREC 3 and FREC 4:

Reduces nausea and vomiting from illness, opioids, chemotherapy, or motion.

FREUC 5 and L4 AAP

  • Pharmacokinetics:

    • Absorption: Well-absorbed; onset 30 minutes orally, 5–10 minutes IV/IM.

    • Distribution: Widely distributed; crosses placenta; GI tract.

    • Metabolism: Extensively metabolised in the liver.

    • Elimination: Excreted in urine and faeces; half-life of 3–5 hours.

  • Pharmacodynamics

    • Blocks serotonin in the gut and CNS.

    • Reduces nausea and vomiting from illness, opioids, chemotherapy, or motion.

    • Minimal sedation and doesn’t affect airway or breathing.

    • Can prolong QT interval, so caution in cardiac patients or those on QT-prolonging drugs.

side effects - unwanted secondary effects of this drug

  • Hiccups.

  • Constipation.

  • Flushing.

  • Hypotension.

  • Chest pain.

  • Arrhythmias.

  • Bradycardia.

  • Headache.

  • Seizures.

  • Movement disorders.

  • Injection site reactions.

dosage and administration - how much do we give and how do we give it?

NB: Two preparations exist (4 mg in 2 ml and 8 mg in 4 ml). They share the same concentration, that is 2 milligrams in 1 ml.

NBB: Monitor pulse, blood pressure, respiratory rate and cardiac rhythm before, during and after administration.

Adults:

  • Route: Intravenous (SLOW IV injection over 2 minutes)/intramuscular.

  • Initial dose: 4mg

  • Repeat dose: 4mg

  • Dose Interval: 30 minutes

  • Concentration: 2mg/1ml

  • Volume: 2ml

  • Max dose: 8mg

Children:

Please see JRCALC Page for Age guidelines.

legislation and regulations - what legal class of drug is it, who can possess it and who can give it?

Ondansetron is a Prescription-Only Medicine (POM). It is not a Controlled Drug. It is listed in Schedule 17 of the Human Medicines Regulations 2012, which authorises certain healthcare professionals, including paramedics, to administer specific POMs without a prescription.

It is a Prescription-Only Medicine (POM), therefore:

  • POMs would normally require a prescription from an authorised prescriber such as a medical doctor or Advanced Paramedic.

However:

It is listed in Schedule 17 of the Human Medicines Regulations 2012, therefore:

  • Paramedics may possess and administer ondansetron in the course of their duties without needing an individual prescription.

  • Administration must still follow local clinical guidelines, governance processes and organisational policy.

bibliography

  1. British National Formulary 2018. Ondansetron. Available from: https://bnf.nice.org.uk/drug/ondansetron.html (Accessed 28/11/25).

  2. Lactmed: Ondansetron. Available from: https://www.ncbi.nlm.nih.gov/books/NBK500798/pdf/Bookshelf_NBK500798.pdf Last updated 15/5/22. (Accessed 28/11/25).

  3. MHRA Drug Safety Update: Ondansetron: small increased risk of oral clefts following use in the first 12 weeks of pregnancy. Available from GOV.UK. Accessed 1/10/24. 5Ondansetron 2mg/ml solution for injection: Summary of Product Characteristics. Hameln pharma ltd. Ondansetron 2 mg/ml Solution for Injection - Summary of Product Characteristics (SmPC). Available from: https://www.medicines.org.uk/emc/product/6469/smpc#gref (Accessed 28/11/25).

  4. Ondansetron and breastfeeding. Are they compatible? Available from: https://www.e-lactancia.org (Accessed 28/11/25).

  5. Salvucci AA, Squire B, Burdick M, Luoto M, Brazzel D, Vaezazizi R. Ondansetron is safe and effective for prehospital treatment of nausea and vomiting by paramedics. Pre-hospital Emergency Care 2011, 15(1): 34–8. 2.

  6. Use of ondansetron in pregnancy. Date of issue 2020 version 4. Available from: https://uktis.org/monographs/use-of-ondansetron-in-pregnancy/ (Accessed 28/11/25).

  7. Warden CR, Moreno R, Daya M. Prospective evaluation of ondansetron for undifferentiated nausea and vomiting in the prehospital setting. Pre-hospital Emergency Care 2008, 12(1): 87–91.

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