To answer your question as well as i can i must first break down both of these medications. Oxycontin is extended realese Oxycodone ( an opiod analgesic), Fentynal is also a opiod analgesic. In my personal opinion i do not believe a doctor will prescribe these pain managment aids in conjunction as there is great danger of overdose and possibly death with that large amount of opiods in your system. I am also a long term sufferer from back pain and have been prescribed many treatments as well, in my best opinion to truly treat back pain attempt easy rehabilitation to strengthen the back and continue the oxycontin treatment (after 3 months of rehab, the pain in my back[ while still on Oxycontin] has gone from a daily 7-8 to a 3-4 on a scale of ten). Hope I could help from one sufferer to another.