Methadone to Extended‑Release Oral Morphine Conversion Guidelines

Dose Calculation

The total daily methadone dose is 40 mg (10 mg administered four times per day)【1】【2】.
The established morphine‑to‑methadone potency ratio for converting from morphine to methadone is 2 : 1【1】【2】【3】【4】.
Applying this ratio, 40 mg of methadone corresponds to an approximate 80 mg daily dose of extended‑release oral morphine【5】.

Methadone exhibits incomplete cross‑tolerance with other opioids, necessitating dose reductions when switching【5】【6】.
Its long and variable half‑life means substantial drug remains for several days after the last dose, complicating reverse conversions【5】.

Begin with 80 mg extended‑release morphine per day (40 mg every 12 h) as the standard 2 : 1 conversion, while anticipating frequent adjustments【5】【6】.
If incomplete cross‑tolerance is a concern, reduce the calculated dose by 25–50 %, yielding a more conservative starting range of 40–60 mg extended‑release morphine daily【5】【6】.

Provide immediate‑release morphine 10–15 mg every 2–4 h as needed for breakthrough pain during the first 3–7 days【7】.
Monitor the total daily morphine consumption (regular plus breakthrough doses) to guide dose adjustments【7】.
Adjust the extended‑release dose daily based on breakthrough medication use, with expected modifications every 1–2 days as methadone clears from the system【7】【5】.
Anticipate that morphine requirements may increase over 3–7 days as methadone’s residual effects diminish【5】.

Do not rely rigidly on standard equianalgesic tables when converting from methadone, as they tend to underestimate methadone’s potency in chronic use【5】.
Avoid abrupt discontinuation of methadone without adequate morphine coverage to prevent withdrawal and uncontrolled pain【5】.
Recognize that methadone clearance takes 1–2 days for substantial reduction and several days for complete elimination, requiring ongoing dose reassessment beyond the first 24 hours【5】.