A diabetic client who is currently taking metformin is ordered a computerized tomography (CT) scan with contrast. The nurse understands that the client's metformin should be discontinued how many hours before receiving intravenous (IV) contrast?

The correct answer is A: 43 hours. Metformin should be discontinued 48 hours before receiving IV contrast to prevent lactic acidosis. As metformin is excreted primarily through the kidneys, contrast dye can impair kidney function, leading to metformin accumulation and potential toxicity. Discontinuing metformin for 43 hours ensures enough time for the drug to be cleared from the system and minimizes the risk of adverse effects. Choices B, C, and D are incorrect because they do not provide an adequate timeframe for metformin cessation before contrast administration, which could result in serious complications for the diabetic client.