Can Duragesic Fentanyl Patches Be Used Either On Inner Or Outer Arm?

Hi, my mother has just been prescribed Durogesic DTrans patches (fentanyl). She was previously on norspan and it was quite specific about where the patch could be located. This says torso or upper arm - is it outside of arm or can it be inside of arm too? is torso only on front of torso, or back as well? is it ok to locate over the heart? thanks, Sam