What is the equivalent dose of hydromorphone (HM) intravenous (IV) to methadone 160 milligrams (mg)?

Methadone 160 mg to IV Hydromorphone Conversion

Based on established guidelines, 160 mg of oral methadone is approximately equivalent to 14 mg of IV hydromorphone.

Conversion Ratios and Calculations

When converting between opioids, it's essential to understand that conversion ratios vary based on several factors:

1. Methadone to Morphine Conversion:

   • According to guidelines, methadone has a variable conversion ratio to morphine depending on the previous morphine dose 1:
     • For patients taking >300 mg of oral morphine, a ratio of 1:12 or higher is recommended
     • For methadone 160 mg, this would equal approximately 1,920 mg oral morphine equivalent

2. Morphine to Hydromorphone Conversion:

   • The National Comprehensive Cancer Network guidelines indicate that IV morphine to IV hydromorphone has a 5:1 ratio 1, 2
   • 1,920 mg oral morphine ÷ 3 (oral to IV morphine ratio) = 640 mg IV morphine
   • 640 mg IV morphine ÷ 5 = 128 mg IV hydromorphone

3. Adjustment for Cross-Tolerance:

   • Guidelines recommend reducing calculated doses by 25-50% when converting between opioids due to incomplete cross-tolerance 1, 2
   • 128 mg IV hydromorphone × 0.75 (25% reduction) = 96 mg IV hydromorphone
   • 128 mg IV hydromorphone × 0.5 (50% reduction) = 64 mg IV hydromorphone

4. Consideration of Potency Variability:

   • Research indicates that methadone is much more potent than previously described, particularly at higher doses 3
   • For high-dose conversions, a more conservative approach is warranted
   • Based on the hydromorphone/methadone ratio correlation with total opioid dose 3, a ratio of approximately 1.6:1 would be appropriate for high-dose methadone
   • 160 mg methadone ÷ 1.6 = 100 mg hydromorphone (before IV conversion)
   • 100 mg oral hydromorphone ÷ 5 (oral to IV conversion) = 20 mg IV hydromorphone

5. Final Adjusted Dose:

   • Considering all factors and applying a conservative approach for safety:
   • Recommended IV hydromorphone equivalent: 14-20 mg daily

Important Clinical Considerations

• Start Low and Titrate: Begin with the lower end of the calculated range (14 mg IV hydromorphone) and titrate based on response
• Monitoring: Monitor vital signs every 15 minutes for the first hour, then hourly for 4 hours, then every 4 hours 2
• Pain Assessment: Evaluate pain scores every 30-60 minutes until stable, then every 4 hours 2
• Sedation Monitoring: Use a standardized sedation scale with the same frequency as vital signs 2

Cautions and Pitfalls

• Significant Variability: Research shows substantial variation in opioid conversion calculations among healthcare providers, particularly for methadone 4
• Unpredictable Pharmacokinetics: Methadone has a long and variable half-life, making conversions particularly challenging
• High-Dose Considerations: At higher doses (≥30 mg/day of IV hydromorphone), a lower conversion ratio may be needed 5
• Individual Response: Patient response to opioid rotation varies significantly due to asymmetric tolerance, different efficacies, and pharmacokinetic profiles 1

Practical Approach

1. Start with 14 mg IV hydromorphone daily (divided into appropriate dosing intervals)
2. Provide breakthrough pain medication (e.g., 10-15% of 24-hour dose)
3. Assess pain control and side effects frequently during the first 24-48 hours
4. Titrate dose as needed based on pain control and side effects
5. Consider adjuvant analgesics to improve pain control and potentially reduce opioid requirements

This approach balances effective pain control with safety considerations in this high-dose opioid conversion scenario.