Wellington ICU Drug Manual © 2023-26
appendix 6:
Opioid dose equivalence
The opioid doses shown in the table below are therapeutically equivalent doses.
All doses are in milligrams, except Fentanyl which is listed in micrograms.
These data are presented to allow conversion between different opioids and different administration routes.Further notes regarding dose equivalence are presented below the table. Please refer to individual monographs for specific drug information.
Intravenous vs oral dose equivalence table
Fentanyl patch
Use with caution in opioid naive patients. Takes 8-12 hours for effect with residual effect for 14-24 hours after patch removed.
25 mcg patch equivalent to:
- Morphine 50 mg PO over 24 hour period
- Morphine 16 mg IV over 24 hour period
50 mcg patch equivalent to:
- Morphine 100 mg PO over 24 hour period
- Morphine 32 mg IV over 24 hour period
Morphine/methadone conversion ratios
The ratio changes as the morphine dose increases - calculate equianalgesic dose then reduce by 25 - 50%
Ratio of 24-hour oral morphine : oral methadone
- For < 90 mg of morphine = 4:1
- For 91 - 300 mg of morphine = 8:1
- For 301 - 600 mg of morphine = 12:1
Oral methadone : IV/IM methadone = 2:1
Seek expert Pain Team or Palliative Care advice if unsure or complex patient