Is metformin hydrochloride (glucophage xr) nephro toxic?

Not exactly: If you have a moderate degree of renal disease, metformin can cause lactic acidosis, which is very serious. If you do not have renal disease, metformin is quite safe.

No: Metformin is not known to be toxic to the kidneys. The concern may be when a patient has naturally kidney function and they take metformin. That person may then be at (rare, but still documented) risk of a condition called lactic acidosis - a potentially dangerous, body-wide build-up of lactic acid that interferes with the delivery with oxygen.