When do NPH (Neutral Protamine Hagedorn) insulin peaks typically occur?

NPH Insulin Peak Action

NPH (Neutral Protamine Hagedorn) insulin peaks at 6-8 hours after subcutaneous injection. 1

Pharmacokinetic Profile

The complete time-action profile of NPH insulin includes:

• Onset: 1 hour after injection 1
• Peak action: 6-8 hours after injection 1
• Duration: 12 hours 1

This intermediate-acting profile distinguishes NPH from other insulin formulations and has important clinical implications for timing of administration and hypoglycemia risk. 1

Clinical Significance of the Peak

The pronounced peak action of NPH at 6-8 hours creates a significant risk of hypoglycemia if meals are delayed or physical activity is increased during this window. 1 This is why patients using NPH must eat meals at set intervals to avoid hypoglycemia, as the peak action is not related to mealtimes. 1

Comparison with Other Insulins

The peak action of NPH contrasts sharply with:

• Rapid-acting insulins (lispro, aspart): Peak at 1-2 hours 1
• Regular insulin: Peaks at 3-4 hours 1
• Long-acting insulin (glargine): No peak action 1

Practical Applications

Steroid-Induced Hyperglycemia

NPH is specifically recommended for steroid-induced hyperglycemia because its 4-6 hour peak aligns with the peak hyperglycemic effect of morning prednisone. 1, 2 The American Diabetes Association recommends administering NPH concomitantly with intermediate-acting steroids due to this timing relationship. 1

Hospitalized Patients

In elderly hospitalized patients with poor oral intake, NPH carries a threefold higher risk of hypoglycemia compared to basal-bolus regimens with insulin analogs, and should generally be avoided in this setting. 1 The peak action at 8-12 hours creates particular risk when nutrition intake is unpredictable. 1

Common Pitfalls

• Do not assume NPH provides "peakless" basal coverage - its pronounced peak at 6-8 hours makes it fundamentally different from true basal insulins like glargine. 1, 3
• Avoid using NPH as the sole basal insulin in hospitalized patients with variable oral intake - the peak action increases hypoglycemia risk when meals are missed or delayed. 1
• Remember that the disadvantages of intermediate-acting insulin's peak action often outweigh the advantages of tight blood glucose control compared to newer basal insulin analogs. 1