I wouldn't expect any obvious interaction between atenolol and any of the common pain reliever/muscle spasm relaxers other than the obvious additional lethargy. Don't fly a plane with the combo
As we all know, the best place for a bad back is flat out on the sofa and then an additional bit of snooziness is always welcome.
What meds did they give you? I like SOMA (carisoprodyl) for back-pain. Unfortunately it's an ancient drug and some pharmacies don't stock it...the big online drugstore always has it though.
Valium my second choice as a muscle relaxant.
I HATE how spacey Flexeril (generic escapes me) makes me feel and that's often the first one they want to prescribe.