Generic Name

Ondansetron

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Classification

FDA Approved Indications

• Nausea and vomiting induced by chemotherapy
• Nausea and vomiting from radiotherapy
• Postoperative nausea and vomiting

Mechanism of Action

Ondansetron selectively antagonizes serotonin 5-HT3 receptors located peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone, preventing serotonin from binding and reducing nausea and vomiting signals.

Dosage and Administration

Adult: Typically 8 mg orally or IV 30 minutes before chemotherapy or surgery, repeated as needed. For postoperative nausea, 16 mg orally or IV prior to anesthesia.

Pediatric: Dose varies by weight and age; generally 8 mg orally or IV for children over 4 years, with specific dosing guidelines.

Geriatric: Use with caution; no specific dose adjustment, but monitor for adverse effects.

Renal Impairment: Adjusted dose may be necessary; consult specific guidelines.

Hepatic Impairment: Use with caution; dose adjustment recommended.

Pharmacokinetics

Absorption: Rapidly absorbed after oral administration; bioavailability approximately 62%

Distribution: Wide tissue distribution; crosses the blood-brain barrier

Metabolism: Extensively metabolized in the liver via CYP3A4, CYP2D6, and CYP1A2

Excretion: Excreted primarily in urine and feces

Half Life: Approximately 3-6 hours

Contraindications

• Known hypersensitivity to ondansetron or other 5-HT3 antagonists

Precautions

• Use cautiously in patients with QT prolongation or electrolyte abnormalities
• Monitor ECG in at-risk populations
• Use during pregnancy only if clearly indicated
• Lactation: Consider the benefits and risks; may pass into breast milk

Adverse Reactions - Common

• Headache (Common)
• Constipation (Common)
• Dizziness (Common)

Adverse Reactions - Serious

• QT prolongation leading to Torsades de Pointes (Rare)
• Serotonin syndrome (Rare)
• Allergic reactions including anaphylaxis (Rare)

Drug-Drug Interactions

• Other medications that prolong QT interval (e.g., certain antibiotics, antipsychotics)
• Proton pump inhibitors may increase serum levels

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Take medication exactly as prescribed.
• Report any chest pain, irregular heartbeat, or signs of allergic reactions.
• Be cautious if feeling dizzy or headache occurs.
• Do not operate machinery if feeling dizzy.

Special Considerations

Black Box Warnings:

• QT prolongation and serious arrhythmias, including Torsades de Pointes

Genetic Factors: CYP2D6 poor metabolizers may have increased drug levels.

Lab Test Interference: None known.

Overdose Management

Signs/Symptoms: Dizziness, severe constipation, hypotension, fainting, or arrhythmias.

Treatment: Supportive, with ECG monitoring; treat arrhythmias accordingly; activated charcoal may be used if ingestion recent.

Storage and Handling

Storage: Store at room temperature, protected from moisture and light.

Stability: Stable for specified shelf life as per manufacturer instructions.