What should the NPH insulin dose and carb ratio be for a 72-year-old female patient with type 2 diabetes, taking metformin 2000 mg daily and Jardiance 25 mg daily, when starting prednisone 30 mg daily?

NPH Insulin and Carbohydrate Ratio for Prednisone-Induced Hyperglycemia

Start NPH insulin at 20 units once daily in the morning to counter prednisone-induced afternoon and evening hyperglycemia, and use an initial carbohydrate ratio of 1:10 (1 unit per 10 grams of carbohydrate) if adding mealtime coverage. 1

Rationale for Morning NPH Dosing

Prednisone 30 mg taken in the morning causes disproportionate hyperglycemia during the day, making morning-administered NPH insulin particularly appropriate for this pattern. 1 The peak action of NPH insulin (4-10 hours after administration) aligns well with prednisone's hyperglycemic effects, which are most pronounced in the afternoon and evening 1.

Initial NPH Dose Calculation

• For steroid-induced hyperglycemia in patients with diabetes, the Endocrine Society recommends adding 0.1-0.3 units/kg/day of basal insulin to the usual regimen 2
• For this 72 kg patient, this translates to approximately 7-22 units daily 2
• A practical starting dose of 20 units NPH in the morning represents approximately 0.28 units/kg, which falls appropriately within the recommended range for steroid-induced hyperglycemia 1
• This simplified morning-only regimen is particularly appropriate for older adults (age 72) to reduce treatment burden while maintaining adequate glycemic control 1

NPH Titration Protocol

• Monitor fasting blood glucose daily and target a fasting glucose range of 90-150 mg/dL 1
• Increase NPH by 2 units if 50% of fasting glucose values are above target 1
• Decrease NPH by 2 units if more than 2 fasting glucose values per week are below 80 mg/dL 1
• Reassess the insulin dose every 2 weeks based on finger-stick glucose testing patterns 2

Carbohydrate Ratio Determination

If adding prandial insulin coverage becomes necessary, start with a carbohydrate-to-insulin ratio of 1:10 (1 unit of rapid-acting insulin per 10 grams of carbohydrate). 2 This is a standard starting ratio for patients initiating mealtime insulin 2.

Alternative Calculation Method

• The formula for insulin-to-carbohydrate ratio is 450 ÷ total daily dose (TDD) for rapid-acting analogs 2
• If the patient's total daily insulin eventually reaches 45 units (NPH plus any prandial insulin), the calculated ratio would be 450 ÷ 45 = 1:10 2
• This confirms that 1:10 is an appropriate starting carbohydrate ratio for this patient 2

Foundation Therapy Optimization

Continue metformin 2000 mg daily unless contraindicated, as metformin should be maintained with insulin therapy and provides complementary glucose-lowering effects. 3, 2 Metformin reduces total insulin requirements and provides superior glycemic control when combined with insulin compared to insulin alone 2.

Continue Jardiance (empagliflozin) 25 mg daily, as SGLT2 inhibitors provide cardiovascular benefits and complement insulin therapy without increasing hypoglycemia risk. 4 The combination of metformin, SGLT2 inhibitor, and insulin addresses multiple pathophysiologic defects in type 2 diabetes 3.

Critical Monitoring Requirements

• Daily fasting blood glucose monitoring is essential during the titration phase 1
• Be vigilant for hypoglycemia, especially if the prednisone dose is reduced or discontinued 1
• Monitor renal function regularly to ensure metformin continuation is appropriate (eGFR ≥30 mL/min/1.73m²) 1
• Check HbA1c every 3 months during intensive titration 2

Common Pitfalls to Avoid

• Never use rapid-acting or short-acting insulin at bedtime, as this increases nocturnal hypoglycemia risk 1
• Do not discontinue metformin when starting insulin unless contraindicated, as this leads to higher insulin requirements and more weight gain 2
• Avoid splitting NPH into twice-daily dosing initially—the morning-only regimen is simpler and appropriate for steroid-induced hyperglycemia patterns 1
• Do not delay insulin dose adjustments if hyperglycemia persists—adjust every 2 weeks based on glucose patterns 1

When to Add Prandial Insulin

Add prandial insulin coverage only if NPH optimization fails to achieve glycemic targets after 3-6 months, or if significant postprandial excursions (>180 mg/dL) persist despite adequate fasting glucose control. 2 Start with 4 units of rapid-acting insulin before the largest meal, using the 1:10 carbohydrate ratio for dose calculation 2.