Teaching Exercise 2: Converting from oral morphine to fentanyl transdermal
patch
Mr. John Smith, a terminally ill lung cancer patient has pain that is well
controlled on Morphine Sustained Action, 90mg every 12 hours. Mr. Smith is now
unable to swallow and so the Morphine needs to be converted into a transdermal
fentanyl patch. Calculate the hourly dose of the fentanyl patch.
Convert to equivalent dose of fentanyl by dividing total 24 hour oral
dose by 100
(Parenteral Fentanyl is 100 times more potent than oral Morphine)
180 mg / 100 = 1.8 milligrams of fentanyl in 24 hours = 1800 micrograms
of fentanyl
Step 3
Divide the calculated 24 hour dose of fentanyl by 24 to calculate the
hourly dose of fentanyl.
1800 micrograms / 24 = 75 micrograms of fentanyl per hour
Thus the final order should read:
Fentanyl attains therapeutic levels in 13-24 hours. So by applying the
patch with the last dose of the oral morphine the chances of increasing
pain during the drug transition can be avoided.
Apply 75 microgram fentanyl patch concurrently with the last dose of long
acting oral morphine 90mg. Stop long acting oral morphine after applying
patch.
