The revised recommendation is that holding metformin before contrast studies is unnecessary; metformin should only be held for 48 hours after contrast studies to ensure that renal function remains normal. (Metformin given during acute renal failure can theoretically lead to lactic acidosis.)
In the future, if this point needs to be made, googling "metformin" and "contrast" leads to this page from the manufacturer:
The main new point is that there is not any need to stop Glucophage any significant time before contrast administration. The reasoning behind this is as follows:Technorati Tags: Metformin, Glucophage
a) presumably, Glucophage levels in the patient will be fine before the contrast study, so,
b) even if the patient goes into renal failure afterwards, and excretes no further Glucophage for awhile, those levels will simply remain fine unless the patient takes another dose. The important thing is to suspend Glucophage use after the contrast procedure until you are sure that contrast-induced renal failure will not occur. The reasonable time chosen for this observation period is 48 hours.