What is the starting dose of Zofran (ondansetron) per nursing (prn) for adults?

Ondansetron (Zofran) Starting Dose for Adults

The standard starting dose of ondansetron (Zofran) for adults as a PRN medication is 8 mg orally every 8-12 hours, with a maximum of 24 mg per day. 1

Dosing Guidelines by Administration Route

Oral Administration

• Tablets/Oral Dissolving Tablets/Oral Soluble Film: 8 mg per dose 2
• Frequency: Every 8-12 hours as needed 1
• Maximum daily dose: 24 mg 1

Intravenous Administration

• Standard IV dose: 8 mg or 0.15 mg/kg 2
• Administration: Slow IV push over 2-5 minutes 1

Dosing Considerations by Clinical Scenario

Chemotherapy-Induced Nausea and Vomiting

• High emetogenic risk: 8 mg oral twice daily or 8 mg IV 2
• Moderate emetogenic risk: 8 mg oral twice daily or 8 mg IV 2
• Low emetogenic risk: 8 mg oral or IV as needed 2

Radiation-Induced Nausea and Vomiting

• High risk radiation: 8 mg oral or IV before treatment 2
• Moderate risk radiation: 8 mg oral or IV before treatment 2
• Low risk radiation: 8 mg oral or IV as breakthrough therapy 2

Post-Operative Nausea and Vomiting

• Pre-operative prophylaxis: 16 mg oral as a single dose one hour before anesthesia 1
• Post-operative treatment: 8 mg IV or oral as needed 1

Special Population Considerations

Elderly Patients

• No dosage adjustment required for age alone, though careful monitoring is recommended 1, 3

Hepatic Impairment

• Mild to moderate impairment: No dosage adjustment needed 1
• Severe impairment: Maximum daily dose should not exceed 8 mg 1

Renal Impairment

• No dosage adjustment required as renal clearance represents only 5% of overall clearance 1

Clinical Pearls

• Ondansetron begins working within 30 minutes of oral administration; therefore, administer at least 30 minutes before anticipated nausea/vomiting 3
• The oral dissolving tablet formulation is particularly useful for patients who have difficulty swallowing or are at risk for aspiration 4
• Bioavailability of oral ondansetron is approximately 60% compared to IV administration due to first-pass metabolism 3
• Elimination half-life averages approximately 3.8 hours 3

Common Side Effects and Management

• Headache: Most common side effect, usually mild and self-limiting 5
• Constipation: Ensure adequate hydration and consider prophylactic stool softeners 2
• QT prolongation: Use with caution in patients with congenital long QT syndrome or taking other QT-prolonging medications 1

Efficacy Considerations

• Ondansetron has demonstrated superior efficacy compared to placebo in multiple clinical trials 1, 6
• In studies of chemotherapy-induced nausea and vomiting, complete response rates (no emesis) range from 55-66% with oral ondansetron 6
• For breakthrough nausea and vomiting, oral dissolving tablets provide equivalent bioavailability to standard tablets 4

Remember that while these are standard dosing recommendations, clinical judgment should be exercised based on the patient's specific presentation, comorbidities, and concurrent medications.