Switching from transdermal drugs: an observational "N of 1" study of fentanyl and buprenorphine.

The aim of this study was to confirm that the concomitant presence of transdermal fentanyl (TTS FE) and buprenorphine (TTS BU) may be feasible without important consequences, using doses presumed to be equianalgesic. A prospective "N of 1" study was carried out in a sample of volunteers with cancer pain receiving stable doses of TTS FE or TTS BU, with adequate pain and symptom control. In the study design, each patient provided data before and after a switch from one opioid to the other and then back to the previous one. Sixteen patients receiving daily stable doses of 0.6 or 1.2mg of TTS FE were switched to TTS BU using an FE-BU ratio of 0.6-0.8. After three days, the TTS BU patch was removed and TTS FE patch was placed for another three days. Six patients receiving TTS BU were switched to TTS FE and then rotated back to TTS BU with the same dosing considerations. No statistical differences in changes in pain and symptom intensity during switching and between the two different sequences were observed. No significant changes in rescue doses of oral morphine were reported at the same intervals. Cancer patients receiving stable doses of TTS FE or TTS BU can be safely switched to the alternative transdermal opioid. Further studies should be performed to gather data about the use of TTS BU with other opioids, at different doses, and in different clinical conditions.