Which statement best reflects the typical hypoglycemia risk window after administration of isophane insulin (NPH)?

• A. 4 to 12 hours
• B. 1 to 1 ½ hours
• C. 2 to 3 hours
• D. 16 to 18 hours

Answer: (A)

Isophane insulin (NPH) is an intermediate-acting insulin, so it doesn’t act right away and its strongest glucose-lowering effect occurs in the middle of its action. After injection, it begins to work in roughly 1 to 2 hours, but the peak activity—and thus the highest risk of hypoglycemia—typically falls around 6 to 12 hours afterward. Therefore, the period when hypoglycemia is most likely is about 4 to 12 hours post-dose, accommodating some individual variation in how quickly it starts and how long it lasts. The other time windows don’t align with the peak action of NPH: 1–1.5 hours is too early and more characteristic of rapid-acting insulins; 2–3 hours is still pre-peak; 16–18 hours is late in the duration when the insulin effect is waning and hypoglycemia risk is lower, though it can occur in some cases.