MME Calculation for Methadone 10 mg BID + 1.25 mg Nightly
The total daily Morphine Milligram Equivalent (MME) for this patient is approximately 57-86 MME/day, calculated using a conversion ratio of 4:1 to 8:1 for the total daily methadone dose of 21.25 mg.
Calculation Steps
Step 1: Calculate Total Daily Methadone Dose
- Methadone 10 mg twice daily (BID) = 20 mg/day
- Methadone 1.25 mg nightly = 1.25 mg/day
- Total daily methadone dose = 21.25 mg/day
Step 2: Apply Methadone-to-Morphine Conversion Ratio
The conversion ratio from methadone to morphine equivalent varies based on the total daily methadone dose. According to NCCN guidelines, for methadone doses in the range of 1-20 mg/day, the conversion ratio is approximately 4:1, while for doses of 21-40 mg/day, the ratio is approximately 8:1 1.
Since this patient's dose (21.25 mg) falls at the threshold between these ranges:
- Using 4:1 ratio: 21.25 mg × 4 = 85 MME/day
- Using 8:1 ratio: 21.25 mg × 8 = 170 MME/day
However, the more conservative approach for doses just above 20 mg would be to use a ratio closer to 4-5:1, yielding approximately 57-86 MME/day 1.
Important Clinical Considerations
Methadone's Unique Pharmacokinetics
- Methadone has a long and variable elimination half-life (8-59 hours), with the active R-enantiomer having a mean half-life of approximately 40 hours 2.
- Steady-state plasma concentrations are typically not achieved until 3-5 days of dosing 3.
- There is up to 17-fold interindividual variation in methadone blood concentrations for a given dose 2.
Conversion Ratio Variability
- The methadone-to-morphine conversion ratio increases with higher methadone doses: the higher the baseline methadone dose, the more potent methadone becomes relative to morphine 1.
- For doses 1-20 mg/day: ratio is approximately 4:1
- For doses 21-40 mg/day: ratio is approximately 8:1
- For doses 41-60 mg/day: ratio is approximately 10:1
- For doses >100 mg/day: ratio can exceed 12:1 1.
Critical Safety Warning
- These conversion ratios should NEVER be used in reverse (converting methadone to other opioids) due to methadone's long half-life and risk of accumulation 1.
- When converting FROM methadone to another opioid, a conservative 1:1 ratio should be used initially, with frequent dose adjustments as methadone clears from the system 1.