Isophane insulin suspension (NPH, Humulin N) requires monitoring for hypoglycemia. How many hours after administration is this most likely to occur?

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

Answer: (A)

Isophane insulin suspension is an intermediate-acting insulin. It begins to work in about 1–2 hours, reaches its peak effect roughly 6–12 hours after injection, and lasts about 18–24 hours. Hypoglycemia tends to occur when the insulin effect is strongest, i.e., during the peak. That makes the 4–12 hour window the period of greatest risk after administration. The earlier windows are before the peak, when the risk is lower, and the later window is after the peak when the effect is fading.