Opioid Conversion Guide

A practical guide from the University of Alberta Multidisciplinary Pain Clinic.

Instructions: Use this page to help solve the common problem of figuring out how to convert from one opioid to another, or from more than one drug to a new opioid. It should be noted that good generalisable data in this area is hard to get. The table is a simplified composite of published data, clinical impressions and informal consensus.

1. Make a list of the total amounts of each opioid drug currently being taken orally, rectally or transdermally in a 24 hr period. Count milligrams of each drug, whether being given as long- or short-acting preparations, scheduled or breakthrough. Injectable opioids get added in later. If there is only one drug, that's fine!
2. Look at the table below. Multiply the amount of each drug by its bioavailability (column 4), to get a smaller number. This is the number of milligrams that actually gets into the bloodstream. Remember that a 100 MICROGRAM fentanyl patch is 0.1 MILLIGRAMS of fentanyl PER HOUR.
3. Convert each number in your list to IV morphine equivalents, by using column 2. For example, if the bioavailable codeine dose is 100 mg, the IV morphine equivalent is 10mg.
4. If any opioids are being given parenterally, add them to the list at this point, and convert them to IV morphine equivalents as well.
5. Add up the IV morphine equivalents. You should now have a single number in milligrams.
6. Reduce this number by 30%.
7. Select your new drug.
8. Use column 2 to obtain the equivalent parenteral dose of the new drug. For example, if your reduced IV morphine dose was 50mg, the equivalent IV hydromorphone dose is 10mg.
9. Divide this number by the bioavailability of the new drug to get a bigger number, that being the oral 24 hour dose of the new drug. Some rounding of numbers is fine.
10. Divide this dose into long- and short-acting fractions as you see fit.
11. Use these steps as only a starting point. Apply careful clinical judgement and be prepared to adjust the dose of the new drug according to response. Remember that because of incomplete cross-tolerance, the starting dose of the new opioid should be reduced by about 30%.

A simpler scheme, used by the Regional Palliative Care Program. Extracted from Alberta Hospice Palliative Care Resource Manual Second edition (2001).

NB: The table below is a guideline only. Patient-to-patient variability occurs. Patients should therefore be monitored closely when their opioids are being switched.

Note: the ratio from oral to SC / IV is 2:1 on most occasions