# 002 Converting to/from Transdermal Fentanyl, 2nd ed

FAST FACTS AND CONCEPTS #2 (PDF)
Author(s): David E Weissman MD

Quick—what dose of the transdermal fentanyl patch (DuragesicTM) is equianalgesic to a 3 mg/hr morphine continuous infusion? Conversions to and from fentanyl transdermal are notoriously tricky, requiring knowledge of the published conversion data, general opioid pharmacology, and a generous dose of common sense. See also Fast Fact #36 on opioid dose conversions.

Step 1: Calculate the 24 hr morphine dose: 3 mg/hr x 24 hrs = 72 mg IV morphine/24 hrs.

Step 2: Convert the IV dose to the equianalgesic oral morphine dose using a ratio of:
1 mg IV = 3 mg oral. Thus, 72 mg IV = 216 mg po/24 hours.

Step 3: Convert the oral morphine dose to transdermal fentanyl. There are two methods:

  • Method 1 – Standard Table. Look up fentanyl transdermal in the PDR and find the morphine conversion table. It says that 135-224 mg of morphine per 24 hours = 50 mcg/hr patch. Note: this range of morphine is very broad which may result in significant under dosing.
  • Method 2 - Alternate Formula. In 2000, Brietbart, et al published an alternative method, based on the results of a multi-center trial by Donner, et al, that relied on a fixed dose conversion ratio to calculate the fentanyl transdermal dose. Brietbart recommended the ratio of:

o 2 mg oral morphine/24 hr = 1 mcg/hr of transdermal fentanyl—rounded to the nearest patch size. In the case example above, 216 mg of oral morphine per day is approximately equianalgesic to the 100 mcg/hr fentanyl patch.

Note: using this formula, 25 mcg/hr of transdermal fentanyl is roughly equivalent to 50 mg oral morphine/24 hours. This dose may be excessive when used in an opioid naïve patient, particularly the elderly.

Key Considerations

  1. All equianalgesic ratios/formulas are approximations; clinical judgment is needed when making dose or drug conversions.
  2. The risk of sedation/respiratory depression with transdermal fentanyl is probably increased in the elderly or patients with liver and renal impairment due to its long half-life, thus, choose the lower end of the dosing spectrum.
  3. When in doubt, go low and slow, using prn breakthrough doses generously while finding the optimal dosage of a long-acting drug.

Other teaching points about Duragesic:

  • Start at the lowest dose, 12 mcg/hr, in an opioid naïve patient; there is no maximum dose.
  • Therapeutic blood levels are not reached for 13-24 hours after patch application and drug will be continue to be released into the blood for at least 24 hours after patch removal.
  • Opioid withdrawal symptoms can occur during dose conversions—care must be taken to avoid this by use of breakthrough opioids.
  • 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

References

  1. Physicians Desk Reference. Available at http://pdr.net.
  2. Donner B, et al. Direct conversion from oral morphine to transdermal fentanyl. Pain. 1996; 64:527-534.
  3. Payne R, et al. QOL and cancer pain: satisfaction and side effects with Transdermal fentanyl versus oral morphine. J Clinical Oncology. 1998:16:1588-1593.
  4. Breitbart W. An alternative algorithm for dosing transdermal fentanyl for cancer-related pain. Oncology. 2000; 14:695-702.
  5. Gourlay GK. Treatment of cancer pain with transdermal fentanyl. The Lancet Oncology. 2001; 2:165-172.

Fast Facts and Concepts are edited by Drew A. Rosielle MD, Palliative Care Center, Medical College of Wisconsin. For more information write to: drosiell@mcw.edu. More information, as well as the complete set of Fast Facts, are available at EPERC: www.eperc.mcw.edu.

Version History: This Fast Fact was originally edited by David E Weissman MD. 2nd Edition published July 2005. Current version re-copy-edited March 2009; information about the lowest patch dose added.

Copyright/Referencing Information: Users are free to download and distribute Fast Facts for educational purposes only. Weissman DE. Converting to/from Transdermal Fentanyl, 2nd Edition. Fast Facts and Concepts. July 2005; 2. Available at: http://www.eperc.mcw.edu/fastfact/ff_002.htm.

Disclaimer: Fast Facts and Concepts provide educational information. This information is not medical advice. Health care providers should exercise their own independent clinical judgment. Some Fast Facts cite the use of a product in a dosage, for an indication, or in a manner other than that recommended in the product labeling. Accordingly, the official prescribing information should be consulted before any such product is used.

ACGME Competencies: Medical Knowledge

Keyword(s): Pain, Opioids