Hi , welcome to HCM,
In case or renal cell carcinoma
, metastasis in bone specially in the spine is most common.
So, the back pain
you told is particularly a bone pain
Spasmoproxyvone is a drug which is famous for its anti- smooth muscle
pain action. It does not have any effect on pain causing due to disease in bone.
Now, in this condition consult with your treating doctor for adding a centrally acting pain inhibitor like tramadol
group of drug.
And consult for investigations to detect any bony lesion.