Why shouldn't you take metformin based drugs after iv contrast?

It doesn't damage : The kidney, but rarely dye of the IV cob trast damages the kidney, and since metformin is destroyed by the kidney, it will build up in blood stream to toxic levels with resulting high risk of life-threatening side effect so one stops meftformin before the conrast, check kidnet function 2 days later- if normal can restart metformin.