What is the recommended dosage of ondansetron (Emeset) for preventing postoperative nausea and vomiting after a Modified Radical Neck Dissection (MRND)?

Ondansetron (Emeset) Dosage for PONV Prevention After Modified Radical Neck Dissection

The recommended dosage of ondansetron (Emeset) for preventing postoperative nausea and vomiting (PONV) after Modified Radical Neck Dissection (MRND) is 8 mg IV administered before the end of surgery, with possible follow-up doses of 8 mg orally every 8 hours for up to 24 hours postoperatively. 1

Rationale for Ondansetron Use in MRND

MRND is considered a procedure with moderate to high risk of PONV due to:

• Head and neck surgical field
• Potential for prolonged anesthesia
• Postoperative pain management requirements

Dosing Protocol

Initial Dose:

• 8 mg IV ondansetron administered approximately 30 minutes before the end of surgery 1

Maintenance Dosing (if needed):

• 8 mg oral ondansetron every 8 hours for up to 24 hours postoperatively 1
• Alternative: 8 mg oral dissolving tablet or oral soluble film for patients with difficulty swallowing 1

Evidence Strength

The American Society of Anesthesiologists (ASA) guidelines provide strong evidence (Category A1-B) that 5-HT3 antagonists like ondansetron are effective for PONV prophylaxis, specifically noting ondansetron's effectiveness in reducing vomiting and need for rescue antiemetics 1.

Multimodal Approach for High-Risk Patients

For patients with multiple risk factors for PONV:

1. First-line: Ondansetron 8 mg IV before end of surgery 1

2. Consider adding:

   • Dexamethasone 4 mg IV after anesthesia induction 1
   • Avoid dexamethasone in diabetic patients or those receiving immunotherapy 2

3. For rescue therapy (if breakthrough PONV occurs):

   • Use an antiemetic from a different class than those used for prophylaxis 3
   • Options include:
     • Metoclopramide 10 mg IV/oral
     • Promethazine 6.25 mg IV
     • Haloperidol 2 mg IV

Special Considerations

• Timing: Administering ondansetron at the end of surgery has shown better efficacy than pre-induction dosing in some studies 4
• Efficacy: Ondansetron 4 mg has been shown to reduce PONV incidence from 81.5% to 33.3% in similar surgical procedures 4
• Number needed to treat: Approximately 2 patients need to be treated with ondansetron to prevent one case of PONV after radical surgery 4

Common Pitfalls to Avoid

1. Underdosing: Using less than 8 mg IV ondansetron may result in inadequate prophylaxis for major head and neck procedures 1

2. Monotherapy: Relying solely on ondansetron in high-risk patients; combination therapy is more effective 1

3. Delayed administration: Administering ondansetron too early during surgery may reduce its effectiveness during the critical first 24 hours postoperatively 4

4. Inadequate follow-up: Failing to provide rescue antiemetics from a different class if PONV occurs despite prophylaxis 3

By following this evidence-based dosing protocol, you can significantly reduce the risk of PONV after MRND, improving patient comfort, satisfaction, and potentially reducing length of stay and complications.