Adjusting NPH Insulin When Increasing Prednisone from 20mg to 30mg
Increase the NPH insulin dose by 25% (from 16 units to 20 units) when increasing prednisone from 20mg to 30mg, administered in the morning to match the peak hyperglycemic effect of the steroid. 1, 2
Rationale for Dose Adjustment
- Steroid-induced hyperglycemia is dose-dependent, with higher prednisone doses causing proportionally greater insulin resistance and hyperglycemia, predominantly from midday to midnight 3
- NPH insulin is the preferred formulation for managing steroid-induced hyperglycemia because its intermediate-acting profile peaks at 4-6 hours after administration, aligning with the peak hyperglycemic effect of glucocorticoids 1, 2
- A 50% increase in steroid dose (from 20mg to 30mg) typically requires a 25-40% increase in insulin dosing to maintain glycemic control, based on the insulin resistance induced by higher glucocorticoid doses 2, 4
Specific Dosing Algorithm
- Calculate the new NPH dose: Increase from 16 units to 20 units (25% increase), administered in the morning 1, 2
- For patients on high-dose glucocorticoids (≥20mg prednisone), insulin requirements are commonly 40-60% higher than standard dosing due to significant insulin resistance 2, 4
- Administer the entire NPH dose in the morning (between 0600-0800 hours) to coincide with the peak action of the steroid 1, 5
Monitoring and Further Adjustments
- Monitor blood glucose before meals and at bedtime to assess adequacy of the insulin regimen 2, 5
- If persistent hyperglycemia occurs despite the initial increase, titrate the NPH dose upward by 2 units every 3 days until target blood glucose is achieved without hypoglycemia 6, 1
- If hypoglycemia develops, determine the cause and if no clear reason is found, lower the NPH dose by 10-20% 6, 1
- Target blood glucose range should be 100-180 mg/dL for hospitalized patients on steroids 5
Additional Prandial Coverage Considerations
- Add or adjust rapid-acting insulin before meals if postprandial hyperglycemia persists despite adequate NPH dosing 6, 1
- Consider a more aggressive carbohydrate ratio of 1:8 (1 unit per 8 grams of carbohydrate) for patients on higher steroid doses, as insulin resistance increases proportionally 2, 5
- Correction insulin should use a factor of approximately 1 unit for every 20-25 mg/dL above target for patients on high-dose steroids 5
Common Pitfalls to Avoid
- Failing to increase insulin proportionally with steroid dose escalation leads to inadequate coverage of steroid-induced hyperglycemia, particularly from midday to midnight 3, 4
- Using long-acting basal analogs (like glargine) instead of NPH may under-treat daytime hyperglycemia and cause nocturnal hypoglycemia, as their 24-hour duration doesn't match the shorter hyperglycemic effect of daily prednisone 7, 3
- If splitting NPH to twice-daily becomes necessary due to persistent hyperglycemia, use 2/3 of the total dose in the morning and 1/3 in the evening 6, 1