What is the oxycodone (Oxy) dose equivalent to morphine for an adult patient with normal renal function and no history of opioid addiction?

Oxycodone to Morphine Equianalgesic Conversion

The standard equianalgesic conversion ratio is 1.5:1, meaning 1 mg of oral oxycodone equals approximately 1.5 mg of oral morphine, or conversely, 30 mg of oral oxycodone equals 45-60 mg of oral morphine. 1, 2

Established Conversion Ratios

Oral Route:

• The most recent ESMO guidelines (2018) establish an oral morphine to oral oxycodone ratio of 1:1.5 (meaning oxycodone is 1.5 times more potent than morphine) 1
• This translates to: 30 mg oral oxycodone = 45 mg oral morphine 2
• Alternatively expressed: 60 mg oral morphine = 40 mg oral oxycodone 2

Parenteral Route:

• When converting to IV/IM routes, remember that parenteral morphine is approximately 3 times more potent than oral morphine 1, 3
• Therefore: 10 mg IV morphine ≈ 30 mg oral morphine ≈ 20 mg oral oxycodone 4

Clinical Application Algorithm

Step 1: Calculate total daily oxycodone dose

• Add all scheduled and breakthrough doses over 24 hours 1

Step 2: Apply conversion ratio

• Multiply oxycodone dose by 1.5 to get morphine equivalent 1, 2
• Example: 60 mg/day oxycodone × 1.5 = 90 mg/day morphine 2

Step 3: Reduce for incomplete cross-tolerance

• When rotating between opioids, reduce the calculated equianalgesic dose by 25-50% to account for incomplete cross-tolerance and individual variability 1, 2
• This safety reduction prevents overdosing due to unpredictable pharmacokinetic differences between patients 2

Step 4: Divide into appropriate dosing schedule

• For immediate-release morphine: divide total daily dose by 6 (every 4 hours) 1
• For controlled-release morphine: divide total daily dose by 2 (every 12 hours) 1

Critical Considerations for Normal Renal Function

Morphine-specific precautions:

• Morphine produces the active metabolite morphine-6-glucuronide, which is renally cleared and contributes to analgesia 1
• In patients with fluctuating renal function, morphine should be used with caution due to potential accumulation of this metabolite causing neurotoxicity 1, 3
• For stable normal renal function, this is not a concern 1

Oxycodone metabolism:

• Oxycodone has more predictable metabolism than morphine, making titration easier 5
• Oral bioavailability is higher (60-87% vs morphine's lower bioavailability), contributing to the potency difference 5
• The active metabolite oxymorphone contributes to analgesia but is less clinically significant than morphine-6-glucuronide 5, 6

Common Pitfalls to Avoid

Do not use conversion tables bidirectionally:

• The FDA label explicitly warns that conversion ratios to fentanyl are conservative and should not be used in reverse to convert back to other opioids, as this can overestimate doses 4
• The same principle applies to morphine-oxycodone conversions—always recalculate rather than simply reversing the ratio 1, 2

Individual variability is substantial:

• Genetic polymorphisms (particularly CYP2D6) affect oxycodone metabolism significantly 6
• The 1.5:1 ratio represents population averages; some patients may require different ratios 7, 8
• A 3:1 morphine:oxycodone ratio that was equipotent in non-dependent individuals was not equipotent in opioid-dependent patients 8

Onset time differences:

• Oxycodone has a shorter time to onset of analgesia compared to morphine (both IV and oral routes) 7
• This faster onset may influence breakthrough pain management strategies 7

Side Effect Profile Differences

• Oxycodone causes somewhat less nausea, hallucinations, and pruritus than morphine at equianalgesic doses 5
• Both drugs cause constipation, but the incidence is similar 5, 9
• Long-term administration of oxycodone may be associated with less toxicity compared to morphine 5

Practical Example

Converting 30 mg oral oxycodone twice daily (60 mg/day total):

1. Calculate morphine equivalent: 60 mg × 1.5 = 90 mg/day morphine 2
2. Reduce by 25-50% for safety: 90 mg × 0.5-0.75 = 45-67.5 mg/day 1, 2
3. Start with conservative dose: 45 mg morphine/day (e.g., 22.5 mg every 12 hours for controlled-release) 2
4. Titrate upward based on response over 24-72 hours 1