Ondansetron

Provider Level

AEMT/RN/Paramedic

Class

Antiemetic, Serotonin 5-HT3 receptor antagonist.

Mechanism of Action

Selectively antagonizes serotonin 5-HT3 receptors centrally in the chemoreceptor trigger zone and peripherally on vagal nerve terminals, preventing the initiation of the vomiting reflex.

Indications

Prevention and treatment of severe nausea and vomiting.

Contraindications

Known hypersensitivity to the drug or other 5-HT3 receptor antagonists, concomitant use of apomorphine, known prolonged QT syndrome.

Routes

PO, SL, IM, IV, IO

Onset / Duration

Onset: IV/IM rapid (within 10 to 30 minutes), PO/SL 30 to 60 minutes. Duration: 3 to 6 hours.

Adverse Effects

Headache, dizziness, fatigue, constipation, diarrhea, transient QT prolongation, arrhythmias, flushing, rare extrapyramidal symptoms.

Precautions & Interactions

Use with caution in patients with hepatic impairment, severe heart failure, bradycardia, or electrolyte abnormalities (such as hypokalemia or hypomagnesemia) due to the risk of QT prolongation and subsequent Torsades de Pointes.

Special Considerations

Consider ECG monitoring in patients with risk factors for QT prolongation or taking other QT-prolonging drugs. May mask symptoms of progressive ileus or gastric distension. Safe for use in pediatric and pregnant patients when clinically indicated and according to local protocols.