Reduce NPH Insulin Dose by 10–20% Immediately
Your patient is experiencing nocturnal hypoglycemia (glucose 90 mg/dL at 1 AM) while on 47 units of NPH at 8 AM with concurrent prednisone therapy—reduce the NPH dose to 38–42 units immediately to prevent recurrent hypoglycemia. 1
Understanding the Problem
NPH insulin administered at 8 AM peaks approximately 4–6 hours later (midday to early afternoon), which appropriately matches the hyperglycemic effect of morning prednisone 1. However, NPH has a duration of action extending 12–18 hours, meaning residual insulin activity persists into the early morning hours 2. A glucose of 90 mg/dL at 1 AM—while not frank hypoglycemia—sits at the lower end of the acceptable range and signals excessive overnight insulin effect, particularly in a patient on steroids who should have higher insulin requirements during waking hours 1, 3.
The American Diabetes Association recommends that when hypoglycemia occurs (or glucose approaches hypoglycemic levels without clear cause), reduce the corresponding insulin dose by 10–20% without delay 1. For your patient receiving 47 units NPH:
- 10% reduction: 47 × 0.90 = 42 units
- 20% reduction: 47 × 0.80 = 38 units
Start with a 10% reduction (42 units) if this is the first low reading; proceed to a 20% reduction (38 units) if the pattern recurs or if the patient has additional hypoglycemia risk factors (elderly, renal impairment, poor oral intake). 1, 4
Why This Matters in Steroid-Induced Hyperglycemia
Prednisone causes hyperglycemia predominantly from midday to midnight, not overnight 3. The 24-hour metabolic profile studies demonstrate that prednisone suppresses insulin secretion postbreakfast and increases insulin resistance through the afternoon and evening, with effects dissipating overnight 3. Consequently, insulin requirements are highest during waking hours and substantially lower overnight 1, 3.
NPH given at 8 AM provides appropriate coverage for the steroid-induced hyperglycemia peak (noon–8 PM) but delivers excessive basal insulin overnight when prednisone effects have waned 1, 5, 3. This mismatch explains the 1 AM glucose of 90 mg/dL despite adequate daytime control 5.
Monitoring After Dose Reduction
- Check fasting glucose (pre-breakfast) daily to assess overnight insulin adequacy 1
- Check pre-lunch and pre-dinner glucose to ensure daytime coverage remains sufficient after dose reduction 1
- Target fasting glucose 80–130 mg/dL; if fasting glucose rises above 180 mg/dL after dose reduction, increase NPH by 2 units every 3 days 1, 4
- If glucose falls below 70 mg/dL at any time, reduce NPH by an additional 10–20% immediately 1
Alternative: Consider Switching to a Long-Acting Basal Analog
If nocturnal hypoglycemia persists despite NPH dose reduction, transition from NPH to a long-acting basal analog (insulin glargine, detemir, or degludec) 6, 2. Long-acting analogs provide more consistent 24-hour basal coverage with lower risk of nocturnal hypoglycemia compared to NPH 6, 2.
When switching from NPH to a basal analog, start with 80% of the current NPH dose to avoid hypoglycemia during the transition 6. For example, if your patient stabilizes on 42 units NPH, initiate glargine at 34 units once daily (42 × 0.80 = 34) 6.
However, morning NPH remains appropriate for steroid-induced hyperglycemia because its peak action (4–6 hours post-injection) aligns well with prednisone's hyperglycemic effect 1, 5. The key is optimizing the dose to prevent overnight hypoglycemia while maintaining daytime control 1.
Common Pitfalls to Avoid
- Do not ignore borderline-low overnight glucose readings (90 mg/dL at 1 AM) in a patient on steroids—this signals excessive overnight insulin and warrants immediate dose reduction 1
- Do not continue the same NPH dose hoping the problem resolves spontaneously—75% of hospitalized patients who experience hypoglycemia have no insulin dose adjustment before the next administration, perpetuating the problem 4
- Do not add correction insulin or adjust prandial insulin to compensate for excessive basal insulin—the basal dose itself must be reduced 1, 4
- Do not delay dose reduction waiting for multiple low readings—a single unexplained low glucose (or near-low glucose in the context of steroid therapy) justifies immediate adjustment 1
When to Reassess the Entire Regimen
If the patient requires prednisone taper, reduce NPH by an additional 10–20% with each steroid dose reduction to prevent hypoglycemia as insulin requirements decline 1. Conversely, if prednisone dose increases, NPH may need upward titration by 2 units every 3 days based on daytime glucose patterns 1.
Monitor blood glucose every 2–4 hours for the first 24–48 hours after any insulin adjustment to identify patterns of hyper- or hypoglycemia 1. If daytime hyperglycemia emerges after NPH dose reduction (pre-lunch or pre-dinner glucose consistently >180 mg/dL), consider splitting NPH to twice daily (2/3 morning, 1/3 evening) rather than continuing to escalate the morning dose 1, 6.