What is the conversion ratio for intravenous (IV) administration when converting oxycodone to morphine?

Intravenous Oxycodone to Morphine Conversion Ratio

When converting from intravenous oxycodone to intravenous morphine, the conversion ratio is approximately 1:1.5, meaning IV oxycodone is about 1.5 times more potent than IV morphine. 1

Understanding Opioid Potency Relationships

• IV oxycodone requires approximately 30% less medication than IV morphine to achieve equivalent analgesia, as demonstrated in clinical studies of cancer pain management 1
• While oral oxycodone and oral morphine have traditionally been considered to have a 1:1 or 1:1.5 potency ratio, this relationship changes when administered intravenously due to differences in first-pass metabolism 2
• In post-surgical pain studies, IV oxycodone demonstrated higher potency than IV morphine, with patients requiring significantly less oxycodone than morphine to achieve the "first state of pain relief" (13.2 mg vs. 24.9 mg) 3

Route-Specific Conversion Factors

• The average relative potency ratio of oral to intravenous morphine is between 1:2 and 1:3, meaning oral morphine doses should be divided by 2-3 when converting to IV morphine 4
• Similarly, when converting from oral to IV oxycodone, a ratio of approximately 1:2 should be used 5
• When converting between IV opioids, the elimination of first-pass metabolism creates different potency relationships than those observed with oral administration 4

Clinical Application Algorithm

1. Calculate the daily IV oxycodone dose currently being administered
2. Multiply the IV oxycodone dose by 1.5 to determine the equianalgesic IV morphine dose 1, 3
3. Consider patient-specific factors that may require dose adjustment:
   • Elderly patients may require lower doses due to altered pharmacokinetics 6
   • Patients with renal impairment should receive reduced doses of morphine 4
   • Opioid-tolerant patients may require higher doses than calculated 2
4. Start with 75-80% of the calculated equianalgesic dose to account for incomplete cross-tolerance between opioids
5. Titrate as needed based on pain control and side effects

Important Considerations and Pitfalls

• Intravenous administration bypasses first-pass metabolism, significantly altering the potency relationships observed with oral administration 4
• Large interindividual variations exist in morphine pharmacokinetics and dynamics, requiring close monitoring after conversion 6
• When high doses of opioids are involved (≥30 mg IV equivalent), a more conservative conversion ratio may be needed to prevent overdosing 7
• The duration of action for IV morphine is approximately 4 hours, which should guide dosing intervals 6

Special Populations

• In patients with renal impairment, fentanyl or buprenorphine may be safer alternatives to morphine due to reduced risk of metabolite accumulation 4
• For patients requiring continuous parenteral opioids who cannot take oral medication, subcutaneous infusion is often preferred over IV unless specific contraindications exist 4

Remember that while these conversion ratios provide a starting point, careful titration and monitoring for both pain control and side effects remain essential for optimal patient outcomes.