For a 78‑kg adult with type 1 diabetes on dexamethasone 2 mg, currently using insulin glargine (Lantus) 20 U, NPH (neutral protamine Hagedorn) insulin 100 U at 6 pm, insulin‑to‑carbohydrate ratio 1 U per 10 g carbohydrate, daytime insulin sensitivity factor 50 mg/dL per unit, and nighttime insulin sensitivity factor 15 mg/dL per unit, and given the reported glucose readings, what should the insulin‑to‑carbohydrate ratio, glargine dose, and NPH dose be adjusted to?

Insulin Dose Adjustments for Type 1 Diabetes on Dexamethasone with Tube Feeding

This patient requires immediate discontinuation of NPH insulin at 6 pm and a substantial increase in Lantus to approximately 40-50 units once daily, with aggressive upward titration of the insulin-to-carbohydrate ratio to 1:5-1:7 grams to counteract dexamethasone-induced insulin resistance. 1, 2, 3

Critical Context: Dexamethasone-Induced Hyperglycemia

This patient is experiencing severe hyperglycemia driven by dexamethasone 2 mg, which causes profound insulin resistance. The current regimen is fundamentally flawed:

• NPH 100 units at 6 pm is inappropriate for type 1 diabetes 4, 1. Guidelines explicitly state that sliding scale or correctional insulin alone should never be used in type 1 diabetes, and the same principle applies to using NPH as the sole basal insulin in this context 4.

• The Lantus dose of 20 units is grossly inadequate. Recent evidence on dexamethasone-induced hyperglycemia shows that current practice consistently underdoses basal insulin, leading to persistent hyperglycemia requiring excessive reactive bolus insulin 3.

Recommended Insulin Regimen

Basal Insulin (Lantus)

Increase Lantus to 40-50 units once daily (approximately 0.5-0.65 units/kg for this 78 kg patient):

• The FDA label recommends that for type 1 diabetes, basal insulin should constitute approximately one-third of total daily insulin requirements 2
• This patient's glucose readings (367→267→163→243→273 mg/dL) demonstrate persistent hyperglycemia despite 100 units of NPH, indicating total daily insulin needs of 100-150 units
• Discontinue NPH entirely 1, 2. When converting from twice-daily NPH to once-daily Lantus, the recommended initial dose is 80% of total NPH, but this patient needs MORE insulin due to dexamethasone 2, 5
• Lantus provides more stable 24-hour coverage with lower nocturnal hypoglycemia risk compared to NPH 6, 7, 8, 9

Insulin-to-Carbohydrate Ratio (ICR)

Tighten the ICR from 1:10 to 1:5-1:7 grams of carbohydrate:

• The patient consumed 43g CHO at 8 am (requiring 4.3 units at 1:10 ratio) yet glucose rose from unknown baseline to 367 mg/dL by 1400
• At 1800, glucose was 267 mg/dL; after eating 43g CHO at 1900, glucose was 163 at 2100 (likely from the 100 units NPH kicking in), then rebounded to 243 at 2 am and 273 at 7 am
• Dexamethasone typically requires 2-3 times more prandial insulin 3. An ICR of 1:5-1:7 means 6-8.6 units per 43g CHO meal
• For the tube feeding (226g CHO from 6 pm to 6 am = ~19g/hour), calculate bolus coverage: 226g ÷ 5-7 = 32-45 units divided across the feeding period

Correction Factor Adjustments

The current ISF values need revision:

• Daytime ISF of 50 mg/dL per unit is too weak. Change to ISF 30-40 mg/dL per unit
• Nighttime ISF of 15 mg/dL per unit is dangerously aggressive and risks hypoglycemia. Change to ISF 30-40 mg/dL per unit (same as daytime given the dexamethasone effect)

Implementation Algorithm

1. Immediately stop NPH 100 units at 6 pm
2. Start Lantus 45 units once daily (can give at any consistent time, but bedtime is traditional) 2
3. Use ICR 1:6 for all carbohydrate intake (both meals and tube feeding)
4. Apply ISF 1:35 for all correction doses (day and night)
5. Monitor glucose every 4-6 hours initially, then adjust:
   • If fasting glucose >180 mg/dL for 2 consecutive days: increase Lantus by 10-20%
   • If fasting glucose 100-180 mg/dL: maintain dose
   • If fasting glucose <100 mg/dL or any hypoglycemia: reduce Lantus by 10-20%

Critical Pitfalls to Avoid

Do not continue NPH in type 1 diabetes during hospitalization 1. The guideline explicitly recommends continuation of scheduled insulin regimens in insulin-treated patients, but modification is required for nutritional status and severity of illness 1. This patient's regimen was already suboptimal.

Do not rely on reactive bolus insulin alone 3. The recent 2026 study on dexamethasone-induced hyperglycemia demonstrated that underdosing basal insulin and compensating with bolus insulin leads to persistent hyperglycemia in 76% of patients 3.

Adjust for tube feeding appropriately. The 226g CHO overnight requires either continuous insulin coverage or division of bolus doses every 4-6 hours during the feeding 1. Consider giving rapid-acting insulin every 4 hours during tube feeding: 226g ÷ 6 = ~38g per 4-hour period, requiring 6-7 units per dose at ICR 1:6.

Monitor closely for the first 48-72 hours 2. Dexamethasone effects peak 8-12 hours after administration and insulin requirements may fluctuate 3.