What is the recommended aprepitant dosage for preventing chemotherapy‑induced nausea and vomiting?

Aprepitant Dosage for Prevention of Chemotherapy-Induced Nausea and Vomiting

For adults and pediatric patients 12 years and older receiving highly or moderately emetogenic chemotherapy, administer aprepitant 125 mg orally on Day 1 (one hour before chemotherapy), followed by 80 mg orally on Days 2 and 3. 1

Standard Dosing Regimen

Highly Emetogenic Chemotherapy (HEC)

• Day 1: Aprepitant 125 mg orally (1 hour before chemotherapy) + 5-HT3 antagonist + dexamethasone 12 mg
• Days 2-3: Aprepitant 80 mg orally (in morning if no chemotherapy) + dexamethasone 8 mg
• Day 4: Dexamethasone 8 mg only 2, 3, 1

Moderately Emetogenic Chemotherapy (MEC)

• Day 1: Aprepitant 125 mg orally (1 hour before chemotherapy) + 5-HT3 antagonist + dexamethasone 12 mg
• Days 2-3: Aprepitant 80 mg orally (in morning if no chemotherapy)
• No dexamethasone on Days 2-3 for MEC 4, 1

Critical Dexamethasone Adjustment

The dexamethasone dose must be reduced by 50% when co-administered with aprepitant because aprepitant inhibits CYP3A4 metabolism of dexamethasone, causing significantly elevated steroid levels. 2, 4, 1 Without this adjustment, patients receive excessive corticosteroid exposure with increased risk of adverse effects.

Multi-Day Chemotherapy Regimens

For multi-day highly emetogenic chemotherapy (e.g., 5-day cisplatin regimens):

• Aprepitant 125 mg on Day 3 (start of chemotherapy)
• Aprepitant 80 mg on Days 4-7
• Combine with 5-HT3 antagonist (Days 1-5) and dexamethasone (20 mg Days 1-2) 2

Important caveat: Evidence for extending aprepitant beyond Day 3 is limited to phase II data and a single phase III study in germ cell tumors. 2, 3 The efficacy benefit of Days 4-5 dosing remains uncertain, though safety data support this approach. 3

Postoperative Nausea and Vomiting (PONV)

For PONV prevention in adults, administer a single 40 mg dose within 3 hours prior to anesthesia induction. 1 This is a completely different dosing paradigm from CINV prevention.

Administration Details

• Can be taken with or without food - food increases AUC by only 9-20%, which is not clinically significant 1, 5
• Swallow capsules whole - do not open or crush 1
• Bioavailability is 59% for 125 mg capsules and 67% for 80 mg capsules 5

Common Pitfalls to Avoid

1. Drug interactions: Aprepitant is both a CYP3A4 inhibitor (Days 1-3) and inducer (Days 4-28). This affects numerous medications including:

   • Hormonal contraceptives (reduced efficacy for 28 days after last dose - use backup contraception) 1
   • Warfarin (monitor INR closely, especially Days 7-10) 1
   • Chemotherapy agents metabolized by CYP3A4 (potential for altered efficacy/toxicity) 6

2. Contraindication: Never use with pimozide due to risk of serious cardiovascular events 1

3. Chronic use: Not recommended for continuous daily administration - only studied for intermittent use with chemotherapy cycles 1

4. Pediatric patients under 12 years: Weight-based dosing required (3.0 mg/kg up to 125 mg on Day 1, then 2.0 mg/kg up to 80 mg on Days 2-3) 7

Evidence Quality

The 125 mg/80 mg/80 mg regimen has Category 1 evidence for single-day HEC and MEC regimens. 2, 8 This dosing was established through dose-ranging studies showing superior efficacy compared to both lower doses (40/25 mg) and similar efficacy to higher doses (375/250 mg) but with better tolerability. 9 The regimen achieves consistent daily plasma exposures and complete response rates of 71-83% in the acute phase and 73% in the delayed phase. 7, 10, 9