Which of the following is an intermediate-acting insulin?

Intermediate-acting insulin is primarily used to help control blood glucose levels for a longer period compared to rapid-acting insulins. NPH (Humulin N) is classified as an intermediate-acting insulin because it has a duration of action typically ranging from about 10 to 20 hours and begins to work roughly 1 to 3 hours after injection. This makes it suitable for providing basal insulin coverage throughout the day and night.

Rapid-acting insulins like Lispro (Humalog) and Glulisine (Apidra) are designed to start working quickly, usually within 15 minutes, and are primarily used around mealtimes to control postprandial (after eating) blood sugar spikes. On the other hand, Lantus is a long-acting insulin that provides a steady level of insulin over a 24-hour period without a pronounced peak, which is different from what is expected of intermediate-acting insulins. Thus, when considering the timing and duration of action, NPH is correctly identified as an intermediate-acting insulin.