What is the equivalent dosage of oxycodone (generic name for OxyContin) for a patient converting from 0.5mg of fentanyl (synthetic opioid analgesic)

Oxycodone Equivalent to 0.5mg Fentanyl

For a patient on 0.5mg (500 mcg) of fentanyl daily, the equivalent oxycodone dose is approximately 800 mg/day, but you should reduce this by 25-50% when converting, resulting in a starting dose of 400-600 mg oxycodone daily due to incomplete cross-tolerance. 1

Conversion Calculation Process

Step 1: Convert fentanyl to morphine milligram equivalents (MME)

• Using the CDC conversion factor of 2.4 for fentanyl (measured in mcg/hr for transdermal, but applicable to total daily dose calculations): 1, 2
• 500 mcg fentanyl × 2.4 = 1,200 MME/day 1, 2

Step 2: Convert MME to oxycodone

• Using the CDC conversion factor of 1.5 for oxycodone: 1, 2
• 1,200 MME ÷ 1.5 = 800 mg oxycodone daily 1, 2

Step 3: Apply dose reduction for incomplete cross-tolerance

• Reduce the calculated dose by 25-50% to account for incomplete cross-tolerance and individual pharmacokinetic variability: 1, 2
• 800 mg × 0.5 (50% reduction) = 400 mg oxycodone daily 1
• 800 mg × 0.75 (25% reduction) = 600 mg oxycodone daily 1

Critical Safety Considerations

This represents an extremely high opioid dose that carries significant overdose risk:

• The CDC notes that doses above 90 MME/day are associated with progressively increased overdose risk, and 1,200 MME represents a potentially life-threatening dose for non-tolerant patients 1, 3
• Monitor the patient continuously for at least 24-72 hours after initiating oxycodone, with particular attention to respiratory depression 4
• Have naloxone immediately available and be prepared to provide respiratory support 3

Practical Dosing Algorithm

For a conservative and safer approach:

• Start with 400 mg oxycodone daily (50% dose reduction), divided into doses every 4-6 hours 1, 4
• This equals approximately 65-70 mg every 4 hours or 100 mg every 6 hours 4
• Provide rescue doses of 10-20% of the 24-hour dose (40-80 mg) every 4-6 hours as needed for breakthrough pain 1
• Reassess pain control and adverse effects within 24-48 hours and titrate based on response 1, 5

Common Pitfalls to Avoid

• Do not use the calculated 800 mg dose directly without dose reduction—this is a mathematical estimate only and does not account for incomplete cross-tolerance 1
• Do not assume 1:1 cross-tolerance between opioids—individual variability in genetics and pharmacokinetics is substantial 1, 6
• Account for the patient's renal and hepatic function, age, prior opioid exposure, and reason for switching (poor pain control vs. adverse effects) 1, 2, 7
• If the patient was poorly controlled on fentanyl, you may start closer to 100% of the calculated dose (600-800 mg), but if pain was well-controlled, always reduce by 50% 1
• Inadequate monitoring after conversion is a critical error—close observation is essential to ensure adequate pain control while avoiding respiratory depression 2, 3