Dear Jane, Hi & Welcome. These medicines can cause harmful interactions if taken together, hence it should be avoided. All these medications are opioid analgesics that are used to treat moderate to severe pain. Oxynorm (Oxycodone) if taken along with Plaexia ((Tapentadol) may increase side effects such as excessive drowsiness, confusion, and difficulty concentrating. This combination may also experience impairment in thinking, judgment, and motor coordination thus resulting in falls and increased risk of injuries. There is no documented harmful interactions between Oxynorm with Fentanyl patch. Using Fentanyl patch together with Palexia can increase the risk of a rare but serious condition called the serotonin syndrome , which is characterized by hallucination, seizure, extremely high BP, increased heart rate, fever, excessive sweating, shivering, blurred vision, severe muscle stiffness, tremor, incoordination, and in severe cases may result in coma and even death. So, in view of the above you can take Oxynorm alone for the relief of chronic back pain. Hope these answer your query. A feed back is appreciated.