What is the oral morphine (morphine) equivalent dose of 180 mg of methadone (methadone)?

Converting 180 mg of Methadone to Oral Morphine Equivalent

180 mg of oral methadone is equivalent to approximately 1,458 mg of oral morphine, using the conversion ratio of 1:8.1 for this dose range. 1

Methadone to Morphine Conversion Process

The conversion from methadone to morphine requires careful consideration due to methadone's unique pharmacological properties. Unlike converting from morphine to methadone, where the ratio varies based on the morphine dose, converting from methadone to morphine uses different principles.

Key Conversion Factors

• For converting methadone to morphine, the National Comprehensive Cancer Network (NCCN) guidelines indicate that a conversion ratio of approximately 1:8.1 is appropriate for methadone doses in the range of 180 mg 1
• This ratio means that each 1 mg of methadone is equivalent to approximately 8.1 mg of oral morphine

Calculation

For 180 mg of methadone:

• 180 mg methadone × 8.1 = 1,458 mg oral morphine equivalent

Important Clinical Considerations

Pharmacological Complexities

• Methadone has a long and variable half-life (8-59 hours) compared to morphine (2-3 hours)
• Methadone accumulates in tissues with repeated dosing, which contributes to its complex pharmacokinetics
• The conversion from methadone to other opioids is particularly challenging due to methadone's unique receptor activity profile

Safety Precautions

• When switching from methadone to morphine, it's crucial to monitor for:

  • Withdrawal symptoms (due to methadone's long half-life)
  • Excessive sedation (if morphine dose is too high)
  • Inadequate pain control (if morphine dose is too low)

• The NCCN guidelines specifically caution that conversion ratios used for morphine-to-methadone should NOT be used in reverse when converting from methadone to other opioids 1

Clinical Monitoring

• On the first day of conversion from methadone to morphine, a conservative ratio of 1:1 may be used initially, with supplemental short-acting opioids as needed
• As methadone is cleared from the body (which takes several days due to its long half-life), morphine doses will likely require frequent adjustments (every 1-2 days)
• Doses should be adjusted toward the higher conversion ratios as methadone is cleared from the system

Practical Application

When transitioning a patient from 180 mg daily methadone to oral morphine:

1. Calculate the total morphine equivalent (1,458 mg)
2. Consider starting with a lower dose (using a more conservative ratio) and titrating up
3. Divide the total daily morphine dose into appropriate dosing intervals based on the formulation used
4. Monitor closely for efficacy and adverse effects
5. Adjust as needed based on clinical response

Remember that these conversions are estimates and individual patient response may vary significantly based on factors such as age, renal/hepatic function, and prior opioid exposure.