NPH Insulin Duration of Action
NPH insulin has a duration of action of approximately 12 hours according to current clinical guidelines, though some research suggests effects may persist up to 24 hours in certain patients. 1
Pharmacokinetic Profile
The time-action characteristics of NPH insulin follow a predictable pattern:
- Onset of action: 1-3 hours after subcutaneous injection 1, 2
- Peak effect: 6-8 hours (with a range of 4-8 hours reported) 1, 2
- Duration of action: 12 hours per guideline recommendations 1
Important Clinical Context
The intermediate-acting profile creates specific clinical implications that differ substantially from true basal insulins:
- NPH has a pronounced peak at 6-8 hours, which creates significant hypoglycemia risk if meals are delayed or physical activity increases during this window 1
- Patients must eat meals at set intervals to match the peak action, as the insulin effect is not meal-related 1
- NPH should never be assumed to provide "peakless" basal coverage like glargine or other long-acting analogs—this is a critical distinction 1
Variability in Duration
While guidelines cite a 12-hour duration, research evidence shows considerable variability:
- Studies using glucose clamp methodology estimated NPH duration at approximately 13 hours with a 25-unit dose 2
- Older research in insulin-treated diabetics found durations ranging from 20-29 hours (mean 25.1 hours), though this likely reflects residual effects rather than clinically significant action 3
- The practical clinical duration for dosing purposes remains 12 hours, requiring twice-daily administration for continuous coverage 1
Comparison to Other Insulin Types
Understanding NPH's profile relative to other insulins helps contextualize its use:
- Rapid-acting insulins (lispro, aspart): Peak at 1-2 hours 1
- Regular insulin: Peak at 3-4 hours 1
- Long-acting insulins (glargine): No peak action, true 24-hour duration 1, 4
Common Pitfalls to Avoid
- Do not use NPH as sole basal insulin in hospitalized patients with variable oral intake, as the peak action dramatically increases hypoglycemia risk when meals are missed or delayed 1
- 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 1
- The 12-hour duration necessitates twice-daily dosing for patients requiring continuous basal coverage—once-daily NPH administration leaves significant gaps in insulin action 5