A 78-year-old patient on chlorpropamide and regular insulin develops severe hypoglycemia after overnight fasting. What is the most likely cause?

A 78-year-old patient on chlorpropamide and regular insulin develops severe hypoglycemia after overnight fasting. What is the most likely cause?

• A. Insulin
• B. Chlorpropamide
• C. Hypovolemia
• D. Effect of general anesthesia

Answer: (B)

The key idea is that chlorpropamide, a long-acting sulfonylurea, can cause prolonged hypoglycemia, especially in older patients with reduced organ function. It stimulates continued insulin release from the pancreas and has a long half-life with active metabolites, so its effects can persist into the overnight fast. When combined with regular insulin and faced with fasting, hepatic glucose production is limited and peripheral glucose uptake remains driven by insulin, pushing blood glucose down to dangerously low levels. This makes chlorpropamide the most likely culprit in this scenario. Hypovolemia is not a direct cause of hypoglycemia, and while anesthesia can affect glucose, it isn’t the primary explanation here without an operative context.

The key idea is that chlorpropamide, a long-acting sulfonylurea, can cause prolonged hypoglycemia, especially in older patients with reduced organ function. It stimulates continued insulin release from the pancreas and has a long half-life with active metabolites, so its effects can persist into the overnight fast. When combined with regular insulin and faced with fasting, hepatic glucose production is limited and peripheral glucose uptake remains driven by insulin, pushing blood glucose down to dangerously low levels. This makes chlorpropamide the most likely culprit in this scenario. Hypovolemia is not a direct cause of hypoglycemia, and while anesthesia can affect glucose, it isn’t the primary explanation here without an operative context.