For a 40‑year‑old man weighing 73 kg with type 1 diabetes who is on basal insulin glargine (Lantus) 14 U daily and fixed rapid‑acting insulin (insulin lispro, Novolog) doses of 18 U at breakfast, 14 U at lunch, and 10 U at dinner, and who received dexamethasone 6 mg 24 hours ago requiring an intravenous insulin drip, what should his basal glargine dose, insulin‑to‑carbohydrate ratio (ICR), and insulin sensitivity factor (ISF) be now that he is started on continuous subcutaneous insulin infusion (CSII)?

Insulin Dosing for Type 1 Diabetes Post-Dexamethasone Transitioning to Subcutaneous Therapy

For this 40-year-old with type 1 diabetes transitioning off insulin drip after dexamethasone, calculate total daily dose (TDD) at 0.3 U/kg (21.9 units, round to 22 units) given his reduced GFR of 75 mL/min, distribute as 50% basal (11 units Lantus) and 50% prandial (divided as 4-4-3 units Novolog), with insulin-to-carbohydrate ratio (ICR) of 1:23 and insulin sensitivity factor (ISF) of 82 mg/dL per unit. 1

Rationale for Dosing Calculation

Total Daily Dose Determination

Given this patient's clinical context, the Endocrine Society guideline for hospitalized patients provides the most applicable framework 1:

• Weight-based calculation: 73 kg × 0.3 U/kg = 21.9 units (round to 22 units TDD)
• Why 0.3 U/kg instead of higher doses? The guideline specifically recommends 0.2-0.3 U/kg for patients with GFR <60 mL/min 1. While this patient's GFR is 75, his Cr of 1.24 indicates borderline renal function, warranting conservative dosing to minimize hypoglycemia risk
• Dexamethasone consideration: The patient received dexamethasone 24 hours ago. His insulin drip requirements totaled approximately 42 units over 20 hours, but this was during peak steroid effect. As dexamethasone's hyperglycemic effect wanes (half-life 36-72 hours), aggressive dosing now would cause severe hypoglycemia

Basal-Bolus Distribution

Split the 22 units as 50% basal and 50% prandial 1:

• Lantus (basal): 11 units once daily
• Novolog (prandial): 11 units total, distributed as 4 units breakfast, 4 units lunch, 3 units dinner

This represents a significant reduction from his home regimen (14 units Lantus + 42 units prandial = 56 units total). The reduction is appropriate because:

1. Post-steroid hyperglycemia is resolving
2. His insulin drip requirements were declining (from 6 units/hour to 2 units/hour)
3. Conservative dosing prevents hypoglycemia during transition 1

Insulin-to-Carbohydrate Ratio (ICR)

Calculate ICR using the 500 rule for rapid-acting insulin 2:

• 500 ÷ TDD = 500 ÷ 22 = 1:23 (1 unit per 23 grams carbohydrate)
• This can be simplified to 1:20 for practical use

The AACE guideline confirms this approach, noting that ICR typically ranges from 1:20 (insulin-sensitive) to 1:5 (insulin-resistant) 2. Given his reduced renal function and post-steroid state, starting conservatively at 1:20-1:23 is appropriate.

Insulin Sensitivity Factor (ISF)

Calculate ISF using the 1800 rule for rapid-acting insulin 2:

• 1800 ÷ TDD = 1800 ÷ 22 = 82 mg/dL per unit
• This means 1 unit of Novolog will lower blood glucose by approximately 82 mg/dL

The AACE guideline specifies 1800/TDD for rapid-acting analogs versus 1500/TDD for regular insulin 2. Since this patient uses Novolog (insulin aspart), the 1800 rule applies.

Critical Considerations for Steroid-Induced Hyperglycemia

Why Not Use His Home Doses?

The patient's home regimen (14 units Lantus + 42 units Novolog = 56 units TDD) is inappropriate immediately post-dexamethasone because:

1. Steroid effect is waning: Dexamethasone causes hyperglycemia primarily during its active phase. His declining insulin drip requirements (6→2 units/hour) indicate resolving hyperglycemia
2. Risk of severe hypoglycemia: Returning to full home doses while steroid effect dissipates would cause dangerous hypoglycemia
3. Guideline-based approach: The Endocrine Society explicitly recommends starting at 0.2-0.3 U/kg for patients with renal impairment, not resuming home doses 1

Correction Insulin Scale

Use the "usual" column for correction doses given his insulin requirements on drip 1:

Blood Glucose (mg/dL)	Correction Dose (units)
141-180	4
181-220	6
221-260	8
261-300	10
301-350	12
351-400	14
≥400	16

Add correction dose to scheduled prandial insulin. At bedtime, give half the correction dose 1.

Titration Strategy

Increase Lantus by 2 units every 3 days if fasting glucose remains >130 mg/dL without hypoglycemia 3. Target fasting glucose 70-130 mg/dL.

Adjust prandial doses based on 2-hour postprandial glucose:

• If consistently >180 mg/dL after specific meals, increase that meal's Novolog by 1-2 units
• If hypoglycemia occurs, reduce corresponding dose by 10-20% 3, 1

Common Pitfalls to Avoid

1. Do not resume home doses immediately: This is the most dangerous error. The patient required an insulin drip due to dexamethasone, not because his home regimen was inadequate
2. Do not use "insulin-resistant" correction scale: Despite recent steroid use, his declining insulin requirements indicate he's not currently insulin-resistant 1
3. Monitor closely for 48-72 hours: Dexamethasone's hyperglycemic effect continues to wane. Be prepared to further reduce insulin doses if hypoglycemia occurs
4. Avoid "stacking" corrections: Wait at least 4 hours between correction doses to prevent cumulative hypoglycemia 2

Monitoring Plan

• Check blood glucose before each meal and at bedtime (minimum 4 times daily)
• Reassess TDD after 24-48 hours based on glucose patterns
• Consider continuous glucose monitoring if available 2
• Plan for gradual uptitration toward home doses over 5-7 days as steroid effect fully resolves