For an adult with type 2 diabetes, BMI 41, weight 122 kg, currently on an intravenous insulin infusion of 6 units per hour, what initial subcutaneous insulin glargine (Lantus) dose, insulin‑to‑carbohydrate ratio, and correction factor should be used when transitioning to a basal‑bolus regimen?

Transitioning from IV Insulin Infusion to Subcutaneous Basal‑Bolus Therapy

For an adult with type 2 diabetes, BMI 41, weight 122 kg, currently requiring 6 units/hour of IV insulin, calculate the total 24‑hour IV dose (144 units/day), then initiate subcutaneous insulin glargine (Lantus) at 72 units once daily (50% of the IV total) given 2–4 hours before stopping the infusion, plus 72 units of rapid‑acting insulin divided as 24 units before each of three meals, with an insulin‑to‑carbohydrate ratio of approximately 1:10 and a correction factor of 50 mg/dL per unit.1

Calculating the Initial Subcutaneous Insulin Dose

• The total daily subcutaneous dose equals the 24‑hour IV insulin amount: 6 U/h × 24 h = 144 U/day.1
• Allocate 50% (72 units) to basal insulin (insulin glargine/Lantus) administered once daily.12
• Allocate the remaining 50% (72 units) to prandial insulin (rapid‑acting analog such as lispro, aspart, or glulisine), divided equally among three meals: 24 units before breakfast, lunch, and dinner.12

Critical Timing for Safe Transition

• Administer the first dose of Lantus 72 units subcutaneously 2–4 hours before discontinuing the IV insulin infusion to prevent rebound hyperglycemia and recurrent ketoacidosis.132
• Never stop the IV insulin before giving the basal dose, because long‑acting insulins require 2–4 hours to reach therapeutic plasma concentrations.13
• Continue the IV infusion for an additional 1–2 hours after the subcutaneous basal injection to ensure adequate overlap.1

Insulin‑to‑Carbohydrate Ratio (Carb Ratio)

• Use the 450 rule to calculate the insulin‑to‑carbohydrate ratio: 450 ÷ 144 (total daily dose) ≈ 3 grams of carbohydrate per 1 unit of insulin.2
• A more practical starting ratio for severe insulin resistance is 1 unit per 10 grams of carbohydrate (1:10), which can be titrated based on 2‑hour postprandial glucose readings.23
• Adjust the ratio by 10–15% every 3 days if postprandial glucose consistently exceeds 180 mg/dL or falls below 80 mg/dL.2

Correction Factor (Insulin Sensitivity Factor)

• Calculate the correction factor using the 1500 rule: 1500 ÷ 144 (total daily dose) ≈ 10 mg/dL per unit, meaning each unit of rapid‑acting insulin will lower blood glucose by approximately 10 mg/dL.21
• For a more conservative approach in severe insulin resistance, use 1 unit to lower glucose by 50 mg/dL with a target glucose of 100–150 mg/dL.3
• Correction dose = (Current glucose – Target glucose) ÷ Correction factor.21

Simplified Correction Scale (Pre‑Meal Hyperglycemia)

• Add 2 units of rapid‑acting insulin for pre‑meal glucose >250 mg/dL (in addition to the scheduled 24‑unit prandial dose).12
• Add 4 units of rapid‑acting insulin for pre‑meal glucose >350 mg/dL.12

Basal Insulin (Lantus) Titration Protocol

• Increase Lantus by 2 units every 3 days if fasting glucose is 140–179 mg/dL.12
• Increase Lantus by 4 units every 3 days if fasting glucose is ≥180 mg/dL.12
• Target fasting glucose: 80–130 mg/dL.12
• Critical threshold: When basal insulin approaches 0.5–1.0 U/kg/day (61–122 units for this patient), stop further basal escalation and focus on prandial dose adjustments to avoid "over‑basalization" and excess hypoglycemia risk.12

Prandial Insulin Titration Protocol

• Adjust each meal's rapid‑acting dose by 1–2 units (≈10–15%) every 3 days based on the 2‑hour postprandial glucose reading.12
• Target postprandial glucose: <180 mg/dL.12
• If unexplained hypoglycemia (<70 mg/dL) occurs, reduce the implicated dose by 10–20% immediately.12

Monitoring Requirements During Transition

• Perform capillary glucose checks before each meal and at bedtime (minimum four times daily).12
• Measure fasting glucose daily to guide basal insulin titration.12
• Obtain 2‑hour postprandial glucose after each meal to assess prandial adequacy and guide carb ratio adjustments.2
• Monitor serum potassium every 2–4 hours while transitioning, as insulin drives potassium intracellularly.1
• Target glucose range for non‑critically ill hospitalized patients: 140–180 mg/dL.12

Hypoglycemia Management

• Treat any glucose <70 mg/dL immediately with 15 grams of fast‑acting carbohydrate, recheck in 15 minutes, and repeat if needed.12
• Never administer rapid‑acting insulin as a sole bedtime correction dose, as this markedly increases nocturnal hypoglycemia risk.12
• If hypoglycemia occurs without an obvious cause, reduce the implicated insulin dose by 10–20% promptly.12

Common Pitfalls to Avoid

• Do not rely on sliding‑scale (correction‑only) insulin alone; correction doses must supplement a scheduled basal‑bolus regimen, as sliding‑scale monotherapy is condemned by major diabetes guidelines and yields only 38% of patients achieving mean glucose <140 mg/dL versus 68% with basal‑bolus therapy.12
• Do not discontinue the IV insulin infusion without first overlapping with subcutaneous basal insulin given 2–4 hours earlier; failure to do so is the most frequent cause of recurrent hyperglycemia and ketoacidosis.13
• Do not continue escalating basal insulin beyond 0.5–1.0 U/kg/day without addressing postprandial hyperglycemia, to prevent over‑basalization and associated hypoglycemia.12

Dose Adjustments for High‑Risk Factors

• For elderly patients (>65 years) or those with renal impairment, reduce the initial subcutaneous dose by 20–50% to minimize hypoglycemia risk.12
• For patients with poor oral intake, apply a 20–50% dose reduction and monitor glucose every 4–6 hours.12

Expected Clinical Outcomes

• With properly implemented basal‑bolus therapy, ≈68% of patients achieve mean glucose <140 mg/dL, compared with ≈38% on sliding‑scale alone.12
• The incidence of hypoglycemia does not increase when basal‑bolus regimens are correctly applied versus sliding‑scale monotherapy.12