What is the equivalent dose of methadone for OxyContin (oxycodone) ER?

Oxycodone ER to Methadone Conversion

When converting from OxyContin ER (oxycodone extended-release) to methadone, use a conversion ratio of approximately 3:1 (3 mg of oxycodone equals 1 mg of methadone) for most patients, but this ratio varies based on the total daily oxycodone dose. 1

Conversion Process

The conversion from oxycodone ER to methadone requires careful consideration due to methadone's unique pharmacological properties:

1. Calculate total daily oxycodone dose

   • Add up all oxycodone doses taken in 24 hours

2. Apply appropriate conversion ratio based on total daily dose:

   • For lower doses of oxycodone: use 3:1 ratio 1
   • For higher doses (>300 mg/day): consider higher ratios (4:1 or greater) 2

3. Reduce calculated methadone dose by 25-50% to account for incomplete cross-tolerance 2

4. Divide total daily methadone dose into 3-4 doses per day initially 2

Example Calculation

For a patient taking 60 mg of OxyContin ER daily:

• Total daily oxycodone dose: 60 mg
• Apply 3:1 conversion ratio: 60 ÷ 3 = 20 mg methadone
• Reduce by 25-50% for safety: 10-15 mg methadone daily
• Divide into 3 doses: approximately 3-5 mg methadone every 8 hours

Important Considerations

Methadone's Unique Properties

• Long and variable half-life (15-60 hours) with potential for accumulation 2
• Delayed peak respiratory depression occurring later than peak analgesic effect 2
• QTc prolongation risk, especially at doses >100 mg/day 2
• Unpredictable individual response due to complex pharmacokinetics 2

Safety Precautions

• Start with lower doses than calculated and titrate gradually
• Monitor closely during the first week of conversion due to risk of accumulation
• Consider ECG monitoring for patients with cardiac risk factors or doses >100 mg/day 2
• Avoid rapid titration - methadone dose increases should occur no more frequently than every 5-7 days 2

Risk Factors

• High-dose conversions carry greater risk of overdose
• Elderly patients may require lower doses
• Renal/hepatic dysfunction may require dose adjustment
• Drug interactions are common with methadone (particularly medications affecting QTc interval) 2

CDC Morphine Milligram Equivalent (MME) Considerations

For reference, the CDC provides these conversion factors to calculate MMEs 2:

• Oxycodone: 1.5 (multiply dose by 1.5 to get MME)
• Methadone: 4.7 (multiply dose by 4.7 to get MME)

However, methadone's conversion factor varies by dose 2:

• 1-20 mg/day: factor of 4
• 21-40 mg/day: factor of 8
• 41-60 mg/day: factor of 10
• ≥61-80 mg/day: factor of 12

Monitoring After Conversion

• Assess pain control and side effects daily for first week
• Watch for signs of oversedation or respiratory depression
• Be prepared to adjust dosing based on clinical response
• Provide rescue doses of immediate-release opioid if needed during transition

Common Pitfalls to Avoid

• Using fixed conversion ratios without considering total daily dose
• Failing to reduce calculated dose to account for incomplete cross-tolerance
• Titrating methadone too quickly (accumulation may not be apparent for days)
• Not monitoring for cardiac effects in at-risk patients
• Converting directly to twice-daily dosing (start with more frequent dosing initially)

Remember that methadone should not be the first choice for an extended-release opioid due to its complex pharmacokinetics and potential for serious adverse effects 2.