Morphine Equivalents of Hydromorphone IV and SQ
Intravenous (IV) hydromorphone is approximately 7-8 times more potent than IV morphine, and subcutaneous (SQ) hydromorphone is approximately 5 times more potent than SQ morphine. 1
Specific Conversion Ratios
According to FDA-approved drug information, the following conversion ratios apply:
IV/SQ Hydromorphone to IV/SQ Morphine: 1.3-2 mg hydromorphone = 10 mg morphine 1
- This translates to a potency ratio of approximately 1:5-1:7.7
Oral Hydromorphone to Oral Morphine: 6.5-7.5 mg hydromorphone = 40-60 mg morphine 1
Route-Specific Considerations
IV Administration
- IV hydromorphone has a rapid onset of action
- When converting from IV morphine to IV hydromorphone, use the more conservative ratio (1:7) initially
- For example: 7 mg IV morphine ≈ 1 mg IV hydromorphone
SQ Administration
- SQ hydromorphone follows similar conversion ratios to IV administration
- The FDA drug label specifically lists IM/SC hydromorphone as 1.3-2 mg being equivalent to 10 mg of morphine 1
- This gives a ratio of approximately 1:5-1:7.7
Clinical Applications and Cautions
Incomplete cross-tolerance: When switching between opioids, reduce the calculated dose by 25-50% initially to account for incomplete cross-tolerance 2
Patient factors affecting dosing:
- Age (elderly patients require lower doses)
- Renal/hepatic impairment (start with lower doses)
- Prior opioid exposure (opioid-tolerant patients may need higher doses)
High-dose considerations: At higher doses (≥30 mg/day of IV hydromorphone), the conversion ratio may be lower (approximately 1:10 rather than 1:11.5) 3
Monitoring Recommendations
When administering IV or SQ hydromorphone:
- Monitor vital signs every 15 minutes for the first hour, then hourly for 4 hours, then every 4 hours 2
- Assess pain scores every 30-60 minutes until stable, then every 4 hours
- Monitor sedation level using a standardized scale
- Ensure respiratory rate remains ≥8/min to continue administration 2
Common Pitfalls to Avoid
- Using fixed conversion ratios without considering patient factors
- Failing to reduce calculated doses when switching between opioids
- Not accounting for renal/hepatic impairment
- Inadequate monitoring for respiratory depression, especially with IV administration
Remember that these conversion ratios are guidelines, and clinical response should guide subsequent dosing adjustments while prioritizing patient safety.