Opioid Conversion Guidelines
Standard Conversion Factors
- The Centers for Disease Control and Prevention (CDC) establishes that hydromorphone has a conversion factor of 4, meaning 1 mg of hydromorphone equals approximately 4 mg of morphine milligram equivalents (MME) 1, 2
- Using this conversion, 20 mg hydromorphone is equivalent to approximately 80 mg morphine equivalent 1
- Some clinical practice guidelines suggest a ratio closer to 5:1, which would yield approximately 100 mg morphine equivalent 3, 4
Route-Specific Considerations
- The conversion ratio applies regardless of route (oral, IV, or subcutaneous) when comparing the same routes 3, 4
- For IV to IV conversion, the 4:1 ratio is directly applicable 1
- For oral to oral conversion, the same 4:1 to 5:1 ratio applies 3, 4
Critical Dosing Precautions When Converting
- When converting a patient from hydromorphone to morphine, the calculated equivalent dose should be reduced by 25-50% to account for incomplete cross-tolerance between opioids 3, 4
- If converting 20 mg hydromorphone, start with 40-60 mg morphine rather than the full calculated dose 3, 4
- This dose reduction is essential to prevent overdose due to individual variability in opioid pharmacokinetics 1
Common Pitfalls to Avoid
- The CDC recommends not using calculated MME doses directly for opioid conversion without dose reduction, as this can lead to fatal overdose 1, 2
- Equianalgesic conversions are estimates only and cannot account for individual variability in genetics and pharmacokinetics 1
- Always start lower than the calculated equivalent dose when switching opioids 3, 4
- Monitor closely for signs of inadequate analgesia or opioid toxicity after conversion 3, 4