Which diabetic medication should be held before a CT scan to avoid complications?

Metformin is recommended to be held before a CT scan because of its association with the risk of lactic acidosis, particularly in situations where there is a potential for renal impairment. During a CT scan, especially if contrast material is used, kidney function may be temporarily reduced due to dehydration or the direct effect of the contrast dye.

In patients taking metformin, if renal function is compromised, the accumulation of the drug can lead to lactic acidosis, a serious metabolic complication. Therefore, it's standard practice to withhold metformin for a specified period before and after the use of contrast agents, typically 48 hours, to ensure that renal function is stable before resuming the medication.

Other diabetic medications listed, such as sitagliptin, insulin, and glipizide, do not carry the same risk of lactic acidosis in the context of acute renal function changes associated with contrast media and thus do not require similar precautions before imaging studies involving contrast.