A patient on NPH insulin twice daily reports nocturnal sweating and fasting blood glucose of 55 mg/dL. NPH insulin has a pharmacokinetic peak that contributes to this risk. When does NPH insulin typically peak after subcutaneous injection?

• A 1 to 2 hours, similar to rapid-acting analogs
• B It is peakless, with a flat profile over 24 hours
• C 12 to 16 hours, providing a late postprandial effect
• D 4 to 8 hours, corresponding to the midnight to early morning window ✓

Explanation

NPH insulin is an intermediate-acting insulin with onset at 1 to 2 hours, peak at 4 to 8 hours, and duration of 10 to 16 hours. The peak at 4 to 8 hours after evening injection coincides with the overnight period, explaining nocturnal hypoglycemia. This is why basal analogs like glargine and degludec, which are peakless, are preferred for basal coverage.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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