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Converting from oral morphine to fentanyl transdermal patch

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.

See: Facts about the Fentanyl Transdermal Patch

Solution Steps

Sequential steps

Process

Answer
Step 1: Calculate total dose oral Morphine over 24 hours 2 x 90 mg = 180 mg
Step 2: 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.

 
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