Opioid Conversion: IV Morphine to Oral Oxycodone
Convert morphine 4 mg IV every 4 hours to oral oxycodone 20 mg every 4 hours.
Conversion Calculation
Starting with morphine 4 mg IV every 4 hours:
- Total daily IV morphine dose: 4 mg × 6 doses = 24 mg/day
- Convert IV morphine to oral morphine: Using the standard 1:3 ratio 1, 24 mg IV morphine = 72 mg oral morphine daily
- Convert oral morphine to oral oxycodone: Using the 1:1.5 ratio 2, 72 mg oral morphine ÷ 1.5 = approximately 48 mg oral oxycodone daily
- Divided dosing: 48 mg ÷ 6 doses (every 4 hours) = 8 mg oral oxycodone every 4 hours
However, applying a more conservative approach with the alternative conversion method:
- Using the direct IV morphine to oral oxycodone conversion factor of approximately 1.2:1 3, 24 mg IV morphine × 1.2 = approximately 29 mg oral oxycodone daily
- This translates to approximately 5 mg oral oxycodone every 4 hours
Recommended Starting Dose
Start with oral oxycodone 5-10 mg every 4 hours, with close titration based on response 4. Given the patient is already on scheduled opioids (not opioid-naïve), starting at 10 mg every 4 hours is reasonable, but err on the conservative side initially.
Key Conversion Principles
The NCCN guidelines 1 establish that:
- IV to oral morphine conversion uses a factor of 3 (10 mg IV morphine = 30 mg oral morphine)
- Oral morphine to oral oxycodone uses approximately 1:1.5 ratio
- Critical caveat: "It is safer to underestimate a patient's 24-hour oxycodone dosage than to overestimate" 4
Titration Strategy
- Initial dose: Start with 5-10 mg oral oxycodone every 4 hours around-the-clock 4
- Monitor closely: Assess pain control and side effects within the first 24-72 hours
- Breakthrough dosing: Provide 10-15% of total daily dose as immediate-release oxycodone for breakthrough pain 1
- Upward titration: Increase by 25-50% if inadequate analgesia after 24 hours
Important Clinical Considerations
Pharmacokinetic advantages of oxycodone 5, 6:
- Higher oral bioavailability (60-87%) compared to morphine (20%)
- More predictable metabolism
- Faster onset of action (1 hour vs morphine)
- Reaches steady state within 24 hours (vs 2-7 days for morphine)
Mandatory co-prescribing:
- Laxative regimen: Must be initiated immediately as 60.6% of oxycodone prescriptions lack this 7
- Multimodal analgesia: Combine with non-opioid analgesics (acetaminophen, NSAIDs if appropriate)
Common Pitfalls to Avoid
- Over-conversion: The relative potency varies with dose and duration; chronic dosing shows different ratios than acute conversion 8
- Renal impairment: Both morphine and oxycodone require caution; consider dose reduction by 25-50% if creatinine clearance <30 mL/min 1
- Immediate vs controlled-release confusion: The conversion above is for immediate-release oxycodone every 4 hours; if converting to controlled-release, give every 12 hours at half the calculated total daily dose per administration 4
Monitoring Parameters
- Pain intensity scores every 4 hours initially
- Sedation level (primary safety concern in first 72 hours) 4
- Respiratory rate (maintain >10 breaths/minute)
- Bowel function daily
- Adjust dose if inadequate analgesia or excessive side effects within 24-48 hours