NPH Insulin Dose Adjustment for Prednisone Increase
Increase the NPH insulin dose to 24 units when prednisone is increased from 20 mg to 30 mg daily. This represents a 50% increase in NPH insulin to match the 50% increase in prednisone dose, which is appropriate given the direct correlation between glucocorticoid dose and hyperglycemic effect 1, 2.
Rationale for Dose Adjustment
The insulin requirement increases proportionally with steroid dose escalation. When prednisone increases by 50% (from 20 mg to 30 mg), the NPH insulin should increase by approximately 40-60% to adequately cover the enhanced hyperglycemic effect 2, 3. A 50% increase (from 16 to 24 units) falls appropriately within this range and provides a practical, easily calculated dose 2.
Key Pharmacokinetic Considerations
NPH insulin should be administered in the morning concomitantly with prednisone because NPH peaks at 4-6 hours after administration, which aligns perfectly with the peak hyperglycemic effect of morning prednisone 1, 2.
Prednisone reaches peak plasma levels 4-6 hours after administration but has pharmacologic actions lasting throughout the day, causing disproportionate daytime hyperglycemia that often normalizes overnight 1, 3.
The degree of hyperglycemia directly correlates with steroid dose—higher doses cause more significant blood glucose elevations, necessitating proportional insulin increases 3.
Monitoring Protocol
Blood glucose monitoring should occur every 2-4 hours initially, with particular attention to afternoon and evening values when steroid effect peaks 2, 3. Target blood glucose range should be 80-180 mg/dL (4.4-10.0 mmol/L) 1, 2.
Do NOT rely solely on fasting glucose measurements, as this will miss the peak hyperglycemic effect of prednisone and underestimate the severity of hyperglycemia 3.
Monitor glucose 2 hours after lunch (around 2-3 PM) as this captures the peak steroid effect 3.
Subsequent Dose Adjustments
If hyperglycemia persists despite the initial increase, increase NPH by 2 units every 3 days until target blood glucose is achieved without hypoglycemia 2, 4.
If hypoglycemia occurs, reduce the NPH dose by 10-20% after determining there is no other clear cause 2, 4.
For higher doses of glucocorticoids, insulin requirements may increase by 40-60% above standard dosing, and sometimes extraordinary amounts of prandial and correctional insulin are needed in addition to NPH 1, 3.
Common Pitfalls to Avoid
Avoid relying solely on long-acting basal insulin without adding or adjusting NPH, as this leads to inadequate coverage of daytime hyperglycemia characteristic of prednisone therapy 2.
Do not delay insulin dose increases when prednisone is escalated—the hyperglycemic effect begins immediately and requires prompt insulin adjustment 3.
Using only sliding-scale correction insulin is associated with poor glycemic control and has been discouraged in guidelines 3.
Remember that insulin requirements will decrease rapidly if prednisone is subsequently tapered or discontinued, requiring prompt dose reductions to avoid hypoglycemia 2, 3.