Ondansetron Drug Therapy Protocol

Clinical Indications and Contraindications

  • Indications for Use

    • Ondansetron is indicated for patients experiencing significant nausea AND / OR vomiting.

  • Absolute Contraindications

    • Known allergy AND / OR Adverse Drug Reaction to ondansetron.

    • Congenital long QT Syndrome.

    • Current apomorphine therapy (typically used in the treatment of Parkinson's disease).

    • Pediatric patients less than 22 years old.

  • Relative Contraindications

    • First trimester pregnancy: Administration may only be considered for cases of extreme and uncontrolled hyperemesis.

  • Precautions

    • Hepatic impairment.

    • Elderly patients.

    • Intestinal obstruction.

    • Patients with identified risk factors for QT interval prolongation or cardiac arrhythmias.

Pharmacology and Pharmacokinetics

  • Drug Class

    • Ondansetron is classified as an Antiemetic 5-HT35\text{-HT}_3 antagonist.

  • Mechanism of Action

    • Ondansetron acts as a serotonin 5-HT35\text{-HT}_3 receptor antagonist.

    • It functions by blocking the action of serotonin, which is a natural substance in the body that may cause nausea and vomiting.

  • Metabolism and Excretion

    • The majority of circulating ondansetron is metabolized in the liver.

    • Excretion is primarily carried out by the kidneys.

  • Pharmacokinetic Profile

    • Onset of Action: Approximately 5 mins5\,\text{mins} when administered via the intravenous (IV) route.

    • Duration of Action: The effects last for several hours.

Presentation and Administration

  • Available Forms (Presentation)

    • Ampoule containing 4 mg/2 ml4\,mg/2\,ml.

    • Orally disintegrating tablet (ODT) containing 4 mg4\,mg.

  • Routes of Administration (ACP2)

    • Oral: via Orally Disintegrating Tablet (PO ODT).

    • Intramuscular (IM).

    • Intravenous (IV).

Dosage Guidelines for Adults

  • PO/IM Dosage

    • The dose for Oral or Intramuscular administration is 4−8 mg4-8\,mg.

  • IV Dosage and Technique

    • The dose for Intravenous administration is 4−8 mg4-8\,mg.

    • The medication must be delivered as a slow push over a period of 2−3 minutes2-3\,\text{minutes}.

  • Dosage Limits and Intervals

    • The total maximum dose is strictly 8 mg8\,mg.

    • Ondansetron must not be administered within 8 hours8\,\text{hours} of a previous dose of the same medication.

Special Clinical Notes

  • Preferred Administration Route

    • An IV cannula should not be inserted for the sole purpose of administering ondansetron.

    • ODT (Orally Disintegrating Tablet) ondansetron should always be considered the preferred option for administration.

  • Adverse Effects and Safety

    • Transient adverse effects have been reported when the medication is delivered via rapid IV administration; hence the requirement for a slow push.

    • Following any IV medication administration, all cannulas should be flushed with sodium chloride.

  • Protocol Reference

    • To review the full drug therapy protocol, practitioners should refer to the Queensland Ambulance Service: Clinical Practice Manual- DTP Ondansetron, 20242024.