How should I dose rapid‑acting insulin for lunch and dinner in an adult patient on 60 mg prednisone daily and 20 units NPH insulin at 8 am, using a 1‑unit‑per‑10‑g carbohydrate ratio, given pre‑meal glucose of 201 mg/dL at noon and 325 mg/dL at dinner?

Rapid-Acting Insulin Dosing for Steroid-Induced Hyperglycemia

For this patient on 60 mg prednisone daily with 20 units NPH at 8 AM, you should initiate rapid-acting insulin at lunch and dinner using a combined carbohydrate-counting and correction-dose approach, starting with approximately 6–8 units at lunch and 8–10 units at dinner, then titrating aggressively every 3 days based on 2-hour postprandial glucose readings.

Understanding the Steroid Effect

• High-dose glucocorticoids (60 mg prednisone) primarily cause afternoon and evening hyperglycemia because they increase insulin resistance throughout the day, with peak effect 4–12 hours after morning administration 1.
• The current NPH dose (20 units at 8 AM) provides some midday coverage but is clearly insufficient given the pre-lunch glucose of 201 mg/dL and pre-dinner glucose of 325 mg/dL 1.
• Steroid-induced hyperglycemia typically requires 40–60% increases in prandial and correction insulin beyond baseline needs 1, 2.

Initial Rapid-Acting Insulin Dosing

Lunch Dose Calculation

• Start with 6 units rapid-acting insulin before lunch (0–15 minutes pre-meal) 1.
• This represents approximately 10% of the basal dose (20 units NPH × 10% = 2 units) plus an additional 4 units for the steroid effect 1.
• Add 2 units correction insulin for the pre-lunch glucose of 201 mg/dL (>200 mg/dL threshold) 1, 2.
• Total lunch dose: 8 units rapid-acting insulin (6 units for carbohydrates + 2 units correction) 1.

Dinner Dose Calculation

• Start with 6 units rapid-acting insulin before dinner 1.
• Add 4 units correction insulin for the pre-dinner glucose of 325 mg/dL (>250 mg/dL warrants 2 units; >300 mg/dL warrants an additional 2 units) 1, 2.
• Total dinner dose: 10 units rapid-acting insulin (6 units for carbohydrates + 4 units correction) 1.

Carbohydrate-to-Insulin Ratio Application

• The stated 1:10 ratio (1 unit per 10 grams carbohydrate) is a reasonable starting point but will likely need adjustment upward due to steroid-induced insulin resistance 1, 3.
• For breakfast: The 1:10 ratio typically underestimates morning insulin needs; consider using 1 unit per 8 grams carbohydrate at breakfast due to dawn phenomenon and steroid effect 3, 4.
• For lunch and dinner: Start with the 1:10 ratio but expect to increase to 1 unit per 8 grams or even 1 unit per 6–7 grams given the 60 mg prednisone dose 3, 1.

Correction Insulin Protocol

• Pre-meal glucose 201–250 mg/dL: Add 2 units rapid-acting insulin 1, 2.
• Pre-meal glucose 251–350 mg/dL: Add 4 units rapid-acting insulin 1, 2.
• Pre-meal glucose >350 mg/dL: Add 6 units rapid-acting insulin and check for ketones 1, 2.
• These correction doses are in addition to the carbohydrate-coverage dose 1, 2.

Titration Schedule

Every 3 Days

• Increase lunch dose by 2 units if 2-hour post-lunch glucose consistently >180 mg/dL 1.
• Increase dinner dose by 2 units if 2-hour post-dinner glucose consistently >180 mg/dL 1.
• Target 2-hour postprandial glucose <180 mg/dL 1.

Hypoglycemia Response

• If glucose falls <70 mg/dL, treat with 15 grams fast-acting carbohydrate and reduce the implicated meal dose by 10–20% (1–2 units) 1.

NPH Adjustment Considerations

• The current 20 units NPH at 8 AM is likely insufficient for adequate basal coverage throughout the day 1.
• Consider increasing NPH to 24–28 units (increase by 4 units every 3 days) if fasting glucose remains >130 mg/dL 1.
• Alternatively, split the NPH to twice daily (e.g., 14 units at 8 AM and 10 units at bedtime) to provide better afternoon/evening basal coverage, which is particularly important with high-dose steroids 1.
• Morning NPH dosing is specifically recommended for steroid-induced hyperglycemia to match the steroid's peak effect 1.

Monitoring Requirements

• Check glucose before each meal and at bedtime (minimum 4 times daily) 1, 2.
• Check 2-hour postprandial glucose after lunch and dinner to guide prandial insulin titration 1.
• Check fasting glucose daily to guide NPH adjustment 1.

Timing of Rapid-Acting Insulin Administration

• Administer rapid-acting insulin 0–15 minutes before meals for optimal postprandial glucose control 1, 5.
• Ideally 15–20 minutes pre-meal if the patient can tolerate this timing, as pharmacokinetic studies show this reduces postprandial glucose excursions by approximately 30% 5, 4.
• Never administer rapid-acting insulin at bedtime as a sole correction dose, as this markedly increases nocturnal hypoglycemia risk 1, 2.

Critical Pitfalls to Avoid

• Do not rely solely on correction insulin without scheduled prandial doses; the glucose levels of 201 mg/dL and 325 mg/dL indicate the need for both carbohydrate coverage and correction 1, 2.
• Do not delay adding prandial insulin when pre-meal glucose consistently exceeds 180 mg/dL on high-dose steroids 1, 2.
• Do not continue escalating NPH beyond 0.5 units/kg/day (approximately 35–40 units for most adults) without addressing postprandial hyperglycemia with prandial insulin 1.
• Do not use sliding-scale insulin as monotherapy; this approach is condemned by all major diabetes guidelines and leads to dangerous glucose fluctuations 1, 2.

Expected Outcomes

• With properly implemented basal-bolus therapy adjusted for steroid effect, approximately 68% of patients achieve mean glucose <140 mg/dL versus only 38% with sliding-scale alone 1, 2.
• Steroid-induced hyperglycemia typically requires total daily insulin doses 40–60% higher than baseline, so expect to use 10–15 units per meal once fully titrated 1, 2.