What should be the NPH (Neutral Protamine Hagedorn) insulin dose, carb ratio, and correction scale for a 65-year-old male with type 1 diabetes, currently on Lantus (insulin glargine) 8 units, starting prednisone 18 mg daily?

NPH Insulin Dosing for Steroid-Induced Hyperglycemia in Type 1 Diabetes

For this 65-year-old male with type 1 diabetes starting prednisone 18 mg daily, initiate NPH insulin at 8-10 units given in the morning (0.1-0.12 units/kg), maintain his Lantus 8 units for basal coverage, use a carbohydrate ratio of 1:15-20 grams, and implement a correction scale of 1 unit per 50 mg/dL above target starting at 150 mg/dL. 1, 2, 3

Rationale for NPH Addition

• Prednisone causes hyperglycemia predominantly between midday and midnight, with peak plasma levels at 4-6 hours after morning administration, creating afternoon and evening hyperglycemic excursions 1, 4
• NPH insulin peaks at 4-6 hours after administration, making it the preferred formulation for managing steroid-induced hyperglycemia when administered in the morning 1, 2
• The typical glycemic pattern with daily morning prednisone shows normal or mild fasting hyperglycemia, with increasing hyperglycemia during the afternoon and peaking in the evening 1

Specific NPH Dosing Calculation

• Initial NPH dosing for steroid-induced hyperglycemia should be 0.1-0.2 units/kg per day, which for this 87 kg patient equals approximately 8.7-17.4 units 2, 3
• Start conservatively at 8-10 units NPH given in the morning to match the steroid's peak effect while minimizing hypoglycemia risk 2, 3
• For low-dose corticosteroids (prednisone 10-40 mg/day), the recommended starting dose is 0.15 units/kg if eating, which equals approximately 13 units for this patient 3
• A randomized trial demonstrated that NPH-based protocols using 0.15 units/kg for low-dose steroids achieved mean blood glucose of 226 mg/dL versus 269 mg/dL with usual care 3

Basal Insulin Management

• Continue Lantus 8 units daily as this patient has type 1 diabetes and must maintain basal insulin coverage even when adding NPH 1
• It is essential that people with type 1 diabetes continue to receive basal insulin even if feedings are discontinued, to prevent diabetic ketoacidosis 1
• The current Lantus dose of 8 units (0.09 units/kg) is appropriate for basal needs, while NPH will address the steroid-induced afternoon/evening hyperglycemia 2

Carbohydrate Ratio Determination

• Use a carbohydrate ratio of 1:15-20 grams (1 unit of rapid-acting insulin per 15-20 grams of carbohydrate) for meal coverage 1
• The standard calculation for nutritional insulin is 1 unit per 10-15 grams of carbohydrate, but this patient's relatively low total daily dose (8 units Lantus) suggests insulin sensitivity 1
• Start conservatively at 1:20 and adjust based on postprandial glucose monitoring to avoid hypoglycemia 1

Correction Scale Protocol

• Implement a correction factor of 1 unit per 50 mg/dL above target, starting corrections at blood glucose >150 mg/dL 1
• The 1800 rule (1800 ÷ total daily dose) can estimate correction factor: with an anticipated total daily dose of approximately 25-30 units (8 Lantus + 10 NPH + 7-12 units prandial), this yields approximately 1 unit per 60-72 mg/dL 1
• Use 1:50 as a safer starting point given type 1 diabetes and hypoglycemia risk 1

Monitoring and Titration Strategy

• Monitor blood glucose before each meal and at bedtime to assess adequacy of the NPH and prandial insulin doses 1, 2
• Increase NPH by 2 units every 3 days if afternoon/evening glucose remains >180 mg/dL without hypoglycemia 2, 3
• If hypoglycemia occurs, determine the cause and if no clear reason is found, lower the corresponding insulin dose by 10-20% 1, 2
• Pay particular attention to nocturnal glucose monitoring, as NPH can cause overnight hypoglycemia if dosed too aggressively 5, 6

Critical Pitfalls to Avoid

• Never discontinue basal insulin (Lantus) in type 1 diabetes, even when adding NPH for steroid coverage—this risks diabetic ketoacidosis 1
• Avoid using only long-acting basal insulin (glargine/Lantus) to manage steroid-induced hyperglycemia, as it may undertreat daytime hyperglycemia and cause nocturnal hypoglycemia 4
• Do not administer NPH at bedtime for morning prednisone dosing—this mismatches the pharmacokinetic profiles and increases nocturnal hypoglycemia risk 1, 2
• Research shows that NPH and glargine require similar total daily doses for steroid-induced hyperglycemia, but NPH better matches the afternoon/evening hyperglycemic pattern 5

When to Consider Dose Splitting

• If glycemic control remains suboptimal with once-daily morning NPH despite titration to 15-20 units, consider splitting to twice-daily NPH (2/3 morning, 1/3 evening) 1, 2
• This approach may be necessary if evening glucose remains elevated despite adequate morning NPH dosing 2