Background Opioid rotation/switching is common in palliative care, and one of the most common switches is between oral morphine and transdermal fentanyl. The purpose of this review was to highlight the wide variation in equianalgesic doses that exists according to different sources.

Method In January 2016, we reviewed national guidelines and Summaries of Product Characteristics for transdermal fentanyl preparations available in the United Kingdom, to determine recommended equianalgesic doses for oral morphine and transdermal fentanyl.

ResultsSee Table 1. As can be seen from the Table, there can be up to a threefold difference in dose of oral morphine for a specific dose of transdermal fentanyl ie, 12 micrograms/hour=30 mg or 90 mg.

Conclusions This review highlights clinically significant (and potentially dangerous) differences in equianalgesic doses of transdermal fentanyl. We would suggest that there needs to be a national/international consensus on equianalgesic doses for transdermal fentanyl.