Background   Conversions to and from fentanyl transdermal (TD) are notoriously tricky. They require knowledge of the published conversion data, general opioid pharmacology, and careful individualization for each patient. Switching between morphine, hydrocodone, oxycodone, and hydromorphone is well-established and the dosing relationships between those drugs are relatively predictable patient to patient. This is less true of fentanyl — there is wider inter-individual variability in fentanyl’s analgesic potency compared to those other commonly used opioids which has led to a widely different conversion dosing strategies. Published equianalgesic ratios between oral morphine and TD fentanyl for instance vary from 150:1 to 80:1 (1). To give an example using the 150:1 ratio: 100 mg/d of oral morphine would be equivalent to (150÷100)=0.67 mg/d of fentanyl which equates to a 25 mcg/h (670 mcg/24h) patch.  Additionally, some conversion strategies can be confusing to clinicians as they present a fentanyl dose in mg/day when the patch is prescribed in mcg/h. This Fast Fact presents practical strategies for converting to transdermal fentanyl from other opioids. See also Fast Fact #36 on opioid dose conversions.

Example transition to transdermal fentanyl for someone on a 3 mg/hr IV morphine infusion: 

Step 1:  Calculate the 24-hour morphine dose: 3 mg/h x 24h= 72 mg IV morphine.
Step 2:  Convert the IV dose to the equianalgesic oral morphine dose using a ratio of: 1 mg IV = 3 mg oral. E.g., 72 mg IV = 216 mg po/24h.
Step 3:  Convert the oral morphine dose to transdermal fentanyl.  There are two main methods. 

• FDA table.  Look up the FDA prescribing information for transdermal fentanyl (Reference 2, pp 29-30). It says that 135-224 mg of morphine per 24 hours = 50 mcg/hr patch.  This is the table approved by the manufacturer and the FDA. It is a more cautious conversion ratio which generally leads to a lower fentanyl starting dose. With this method, one needs to particularly be prepared to increase the fentanyl dose quickly (after 72h) if it is too low and to expect to rely more heavily on as needed short-acting opioids to treat pain while the patch dose is being optimized. While the FDA table does not use a fixed conversion ratio, it approximates a 150:1 morphine: fentanyl conversion ratio.
• Breitbart Formula.  In 2000, Brietbart and colleagues (3) published an alternative method based on the results of a multi-center trial by Donner and colleagues (4) that relied on a fixed dose conversion ratio to calculate the fentanyl transdermal dose. Brietbart recommended the ratio of:
  • 2 mg oral morphine/24hr = 1 mcg/hr of TD fentanyl, rounded to the nearest patch size. Note the differing units between morphine and fentanyl. In the example above, 216 mg/day of oral morphine is approximately equianalgesic to the 100 mcg/hr fentanyl patch. With this method, one simply halves the total daily morphine mg to approximate the fentanyl patch strength in mcg/hr. 
  • This is a more ‘aggressive’ dosing strategy for converting to fentanyl, and clinicians should watch for oversedation or other fentanyl side effects particularly in days 2-3 of starting the patch. The Breitbart dosing strategy ends up approximately being an 80:1 morphine:fentanyl ratio.
• Which strategy to use? In general, the Breitbart strategy can be appropriate for younger/stronger patients who have severe pain and tolerate opioids well, especially at doses of 100 mg/day oral morphine or less. The more conservative FDA Table strategy is more appropriate for older, frailer patients; patients who are at a higher risk of overdose/harm from opioids (e.g. liver failure, sleep apnea, concomitant benzodiazepine use, etc); and for situations of very high (>100-150 mg/day) oral morphine baseline doses.

Key considerations 

1. When in doubt, go low and slow, using prn breakthrough doses generously while finding the optimal dosage of a long-acting drug.
2. TD fentanyl is prescribed in multiples of 12.5 mcg/hr and calculated ‘equivalent’ doses need to be adjusted to fit the nearest available patch strength.
3. These strategies are not appropriate for converting from methadone or buprenorphine to TD fentanyl.

Other teaching points about transdermal fentanyl: 

• Start at the lowest dose, 12 mcg/hr, in an opioid naïve patient.
• Patients often start feeling the effects of starting transdermal fentanyl around 12 hours. Therapeutic blood levels are not reached for 18-36 hours after patch application and drug continues to be released into the blood for at least 24 hours after patch removal. For someone on a continuous opioid infusion it can be helpful to continue the infusion for at least 6 hours after applying a patch to prevent pain from escalating around hours 6-12. For patients on extended-release oral opioids it can be helpful to have the patient take their last ER opioid pill at the same time as they apply the patch as the pill will be wearing off around the time the fentanyl serum levels are rapidly increasing.
• Some patients will need to have their patches changed every 48 hours.
• The recommended upward dose titration interval is no more frequently than every 72 hours.
• Place patches on non-irradiated, hairless skin. Direct heat applied over the patch can increase drug absorption with increased toxic effects.
• There are no data that cachectic patients have reduced efficacy due to loss of subcutaneous fat; however cachectic patients may require higher dosing (5).

References:   

1. Treillet E, Laurent S, Hadjiat Y. Practical management of opioid rotation and equianalgesia. J Pain Res. 2018;11:2587-2601.
2. Duragesic Prescribing Information. US Food & Drug Administration. http://www.accessdata.fda.gov/drugsatfda_docs/label/2005/19813s039lbl.pdf.  Accessed April 21, 2025.
3. Breitbart W. An alternative algorithm for dosing transdermal fentanyl for cancer-related pain. Oncology.  2000; 14:695-702.
4. Donner B, et al.  Direct conversion from oral morphine to transdermal fentanyl.  Pain. 1996; 64:527-534.
5. Heiskanen T, Matzke S, Haakana S et al. Transdermal fentanyl in cachectic cancer patients. Pain. 2009; 144:218-22. doi: 10.1016/j.pain.2009.04.012.

Version History:  Originally edited by David E Weissman MD.  2nd Edition published July 2005; 3rd Edition May 2015. 4th Edition May 2025.
Conflicts of Interest: None to disclose.