What should be the starting dose of insulin glargine (Lantus), the insulin‑to‑carbohydrate ratio, and the correction factor for a 23‑year‑old woman with type 2 diabetes, weight 122 kg (BMI 41 kg/m²) receiving an intravenous insulin infusion of 6.5 U per hour?

Transition from IV Insulin Infusion to Subcutaneous Basal‑Bolus Therapy

For a 23‑year‑old woman (122 kg, BMI 41) receiving 6.5 U/h IV insulin, initiate subcutaneous insulin with approximately 78 U insulin glargine (Lantus) once daily plus 26 U rapid‑acting insulin before each of three meals, administered 2–4 hours before stopping the IV infusion. 1, 2

Calculating the Total Daily Subcutaneous Dose

• Base the subcutaneous total daily dose (TDD) on the IV insulin infusion rate during the prior 6–8 hours when stable glycemic control was achieved. 1
• For an infusion rate of 6.5 U/h over 24 hours, the total IV insulin delivered is 156 U/day (6.5 U/h × 24 h). 1
• Use 100 % of the 24‑hour IV insulin amount as the initial subcutaneous TDD (156 U/day), because this patient demonstrates severe insulin resistance requiring higher doses. 1, 2

Basal Insulin (Lantus) Dosing

• Allocate 50 % of the TDD to basal insulin: 156 U ÷ 2 = 78 U insulin glargine once daily. 1, 2
• Administer the basal dose 2–4 hours before discontinuing the IV insulin infusion to prevent rebound hyperglycemia and recurrent ketoacidosis. 1, 3
• Continue the IV insulin for 1–2 hours after the subcutaneous basal injection to ensure adequate absorption. 1, 3
• Give Lantus at 20:00 h (8 PM) as the preferred daily injection time to align with transition protocols. 2

Prandial (Rapid‑Acting) Insulin Dosing

• Allocate the remaining 50 % of the TDD to prandial insulin: 156 U ÷ 2 = 78 U total prandial, divided equally among three meals = 26 U before each meal. 1, 2
• Use a rapid‑acting analog (lispro, aspart, or glulisine) administered 0–15 minutes before meals. 1, 2

Carbohydrate‑to‑Insulin Ratio (Carb Ratio)

• Calculate the insulin‑to‑carbohydrate ratio (ICR) using the formula: 450 ÷ TDD. 2
• For a TDD of 156 U: 450 ÷ 156 = ≈ 2.9 g carbohydrate per 1 U insulin (round to 1 U per 3 g carbohydrate). 2
• This ratio means the patient requires 1 U of rapid‑acting insulin for every 3 g of carbohydrate consumed. 2
• Adjust the ICR if post‑prandial glucose consistently misses the target of <180 mg/dL. 2

Correction Factor (Insulin Sensitivity Factor)

• Calculate the insulin sensitivity factor (ISF) using the formula: 1500 ÷ TDD for regular insulin or 1700 ÷ TDD for rapid‑acting analogs. 2
• For rapid‑acting insulin with TDD of 156 U: 1700 ÷ 156 = ≈ 11 mg/dL per 1 U insulin. 2
• This means 1 U of rapid‑acting insulin will lower blood glucose by approximately 11 mg/dL. 2
• Correction dose = (Current glucose – Target glucose) ÷ ISF. 2
• For example, if pre‑meal glucose is 250 mg/dL and target is 125 mg/dL: (250 – 125) ÷ 11 = ≈ 11 U correction dose, added to the scheduled prandial dose. 2

Simplified Correction Scale (Alternative)

• Add 2 U rapid‑acting insulin for pre‑meal glucose >250 mg/dL. 1, 2
• Add 4 U rapid‑acting insulin for pre‑meal glucose >350 mg/dL. 1, 2
• These correction doses are in addition to the scheduled 26 U prandial dose, not a replacement. 1, 2

Monitoring Requirements During Transition

• Check capillary glucose before each meal and at bedtime (minimum four times daily). 1, 2
• Measure fasting glucose daily to guide basal insulin titration. 1, 2
• Obtain 2‑hour post‑prandial glucose after each meal to assess prandial adequacy and guide carb ratio adjustments. 2
• Monitor serum potassium every 2–4 hours during the transition, as insulin drives potassium intracellularly. 1, 3

Basal Insulin Titration Protocol

• Increase Lantus by 2 U every 3 days if fasting glucose is 140–179 mg/dL. 1, 2
• Increase Lantus by 4 U every 3 days if fasting glucose is ≥180 mg/dL. 1, 2
• Target fasting glucose: 80–130 mg/dL. 1, 2
• If unexplained hypoglycemia occurs (glucose <70 mg/dL), reduce the basal dose by 10–20 % immediately. 1, 2

Prandial Insulin Titration Protocol

• Adjust each meal dose by 1–2 U (or 10–15 %) every 3 days based on the 2‑hour post‑prandial glucose reading. 1, 2
• Target post‑prandial glucose: <180 mg/dL. 1, 2

Critical Threshold for Basal Insulin Escalation

• When basal insulin approaches 0.5–1.0 U/kg/day (61–122 U for this patient), stop further basal escalation and intensify prandial insulin instead to avoid "over‑basalization" with increased hypoglycemia risk. 1, 2
• Clinical signals of over‑basalization include basal dose >0.5 U/kg/day, bedtime‑to‑morning glucose drop ≥50 mg/dL, hypoglycemia episodes, and high glucose variability. 2

Hypoglycemia Management

• Treat any glucose <70 mg/dL immediately with 15 g fast‑acting carbohydrate, recheck in 15 minutes, and repeat if needed. 1, 2
• Never administer rapid‑acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk. 1, 2

Adjunctive Therapy Considerations

• Continue metformin at maximum tolerated dose (up to 2,000–2,550 mg/day) unless contraindicated, as this combination reduces total insulin requirements by 20–30 %. 2
• Discontinue sulfonylureas when initiating basal‑bolus insulin to avoid additive hypoglycemia risk. 2

Common Pitfalls to Avoid

• Do not stop the IV insulin infusion without first overlapping with subcutaneous basal insulin administered 2–4 hours earlier—this is the most common cause of recurrent diabetic ketoacidosis. 1, 3
• Do not use sliding‑scale insulin as monotherapy; correction doses must supplement a scheduled basal‑bolus regimen. 1, 2
• Do not continue escalating basal insulin beyond 0.5–1.0 U/kg/day without addressing post‑prandial hyperglycemia, as this leads to over‑basalization with increased hypoglycemia and suboptimal control. 1, 2