Metformin
A biguanide antidiabetic that lowers blood glucose by reducing hepatic glucose production and improving insulin sensitivity.
Exam items lean on the iodinated-contrast scenario: the “tell” is a client on metformin headed for a CT with dye or a cardiac cath. The hinge is renal function plus route — current ACR guidance says a client with normal renal function getting IV contrast usually needs no hold, but with reduced renal function, AKI, or arterial/catheter studies (cardiac cath), hold metformin at the procedure and for 48 hours, then resume only after renal function is rechecked and normal. The dreaded answer is the rare but lethal lactic acidosis: report myalgias, unusual somnolence, unexplained hyperventilation, and abdominal distress — vague symptoms test-writers love to disguise.
The classic trap is confusing it with insulin: metformin alone essentially does not cause hypoglycemia, so “give juice/15 g carbs” is wrong unless a sulfonylurea or insulin is also on board. Don’t expect peak/onset timing here — that’s an insulin distinction. Two sleepers: chronic metformin use can cause vitamin B12 deficiency, and it is withheld in acutely ill clients (sepsis, dehydration, hypoxia) where lactic-acidosis risk climbs.
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