What basal insulin glargine dose, carbohydrate-to-insulin ratio, and correction factor should be used for a 23‑year‑old obese woman with long‑standing type 2 diabetes (BMI 41 kg/m², A1c 13 %) on a high‑rate IV insulin infusion?

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Transitioning from IV Insulin to Subcutaneous Basal‑Bolus Therapy in Severe Hyperglycemia with Ketosis

For this 23‑year‑old woman with long‑standing type 2 diabetes, severe hyperglycemia (A1c 13.0 %), mild ketosis, and current IV insulin infusion at 16 units/hour, initiate Lantus at 96 units once daily at bedtime, start rapid‑acting insulin at 32 units before each of the three main meals, and use a carbohydrate ratio of 1:5 with a correction factor of 1:15.

Calculating the Total Daily Subcutaneous Insulin Dose

  • When transitioning from IV to subcutaneous insulin, the total subcutaneous dose equals half of the IV insulin infused over 24 hours 1.
  • At 16 units/hour, this patient receives 384 units/day via IV infusion; therefore, the initial subcutaneous total daily dose (TDD) is 192 units 1.
  • For severe hyperglycemia (A1c ≥ 9 % or glucose ≥ 300 mg/dL), guidelines recommend starting with 0.3–0.5 units/kg/day as total daily insulin 2, 1.
  • At 122 kg, a dose of 0.3–0.5 units/kg/day yields 37–61 units/day, but this patient's IV insulin requirement of 16 units/hour indicates far greater insulin resistance, necessitating the higher calculated dose of 192 units/day 2, 1.

Basal Insulin (Lantus) Dosing

  • Administer 50 % of the TDD as basal insulin once daily, equating to 96 units of Lantus 2, 1.
  • Give the first subcutaneous basal insulin dose 2–4 hours before stopping the IV infusion to prevent rebound hyperglycemia and recurrent ketoacidosis 1.
  • Alternatively, adding 0.15–0.30 units/kg of basal insulin analog during the IV infusion can shorten infusion duration and further prevent rebound hyperglycemia; for this patient, that would be 18–37 units 1.
  • Administer Lantus at 20:00 h (8 PM) to align with transition from IV insulin and maintain stable basal levels 1.

Prandial Insulin Dosing

  • Deliver the remaining 50 % of the TDD as rapid‑acting insulin divided among three meals, amounting to 96 units total or 32 units per meal 2, 1.
  • Administer rapid‑acting insulin (lispro, aspart, or glulisine) 0–15 minutes before each meal for optimal postprandial glucose control 2, 1.
  • When basal insulin approaches 0.5–1.0 units/kg/day (61–122 units for this patient), adding or intensifying prandial insulin becomes more appropriate than continuing to escalate basal insulin alone 2, 1.

Carbohydrate‑to‑Insulin Ratio (Carb Ratio)

  • Calculate the insulin‑to‑carbohydrate ratio (ICR) using the formula 450 ÷ TDD for rapid‑acting analogs 1.
  • With a TDD of 192 units, the ICR is 450 ÷ 192 = 2.3 grams of carbohydrate per unit, or approximately 1 unit per 2 grams of carbohydrate 1.
  • For practical application, round to 1 unit per 5 grams of carbohydrate initially, then adjust based on 2‑hour postprandial glucose readings 1.
  • A common starting insulin‑to‑carbohydrate ratio is 1 unit per 10–15 grams of carbohydrate, but this patient's severe insulin resistance requires a more aggressive ratio of 1:5 1.

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 1.
  • With a TDD of 192 units, the ISF is 1700 ÷ 192 = 8.9 mg/dL per unit, meaning 1 unit of rapid‑acting insulin lowers glucose by approximately 9 mg/dL 1.
  • For practical application, round to 1 unit per 15 mg/dL above target glucose 1.
  • Add 2 units of rapid‑acting insulin for pre‑meal glucose > 250 mg/dL and 4 units for glucose > 350 mg/dL (simplified sliding scale) 1.
  • Correction insulin must always supplement a scheduled basal‑bolus regimen; it should never be used as monotherapy 1.

Titration Protocols

Basal Insulin Titration

  • Increase Lantus by 2 units every 3 days if fasting glucose is 140–179 mg/dL 2, 1.
  • Increase Lantus by 4 units every 3 days if fasting glucose is ≥ 180 mg/dL 2, 1.
  • Target fasting glucose 80–130 mg/dL 2, 1.
  • If hypoglycemia occurs without clear cause, reduce the current dose by 10–20 % immediately 2, 1.

Prandial Insulin Titration

  • Adjust each prandial dose by 1–2 units (or 10–15 %) every 3 days based on the 2‑hour postprandial glucose reading 2, 1.
  • Target postprandial glucose < 180 mg/dL 2, 1.
  • Adjust the ICR if postprandial glucose consistently misses the target 1.

Monitoring Requirements

  • Check fasting glucose daily during titration to guide basal insulin adjustments 2, 1.
  • Measure pre‑meal glucose immediately before each meal to calculate correction doses 1.
  • Obtain a 2‑hour postprandial glucose to assess prandial adequacy and guide further titration 1.
  • Reassess HbA1c every 3 months during intensive titration 1.
  • For hospitalized patients eating regular meals, perform point‑of‑care glucose checks immediately before each meal and at bedtime 1.

Adjunctive Oral Therapy

  • Continue metformin at the maximum tolerated dose (up to 2,000–2,550 mg/day) unless contraindicated; this combination reduces total insulin requirements by 20–30 % and provides superior glycemic control 1.
  • The patient is currently on metformin 2000 mg daily, which should be continued 1.
  • Discontinue sulfonylureas when initiating basal‑bolus insulin to prevent additive hypoglycemia risk 1.

Addressing Mild Ketosis

  • The anion gap of 17 (normal < 12) and ketones of 1.17 mmol/L indicate mild ketosis, likely from prolonged hyperglycemia and relative insulin deficiency 1.
  • Continuous IV insulin is the standard of care for critically ill patients with diabetic ketoacidosis (DKA), but this patient's mild ketosis without acidosis (bicarbonate 19 mEq/L, normal 22–28) does not meet criteria for DKA 1.
  • When transitioning off IV insulin, give the first subcutaneous basal insulin dose 2–4 hours before stopping the infusion to avoid rebound hyperglycemia and recurrent ketoacidosis 1.
  • Adding 0.15–0.30 units/kg of basal insulin analog during the IV infusion can shorten infusion duration and further prevent rebound hyperglycemia 1.
  • Monitor for resolution of ketosis with aggressive fluid resuscitation and insulin therapy 1.

Expected Clinical Outcomes

  • With appropriately weight‑based basal‑bolus therapy, ≈ 68 % of patients achieve mean glucose < 140 mg/dL, compared with ≈ 38 % on sliding‑scale alone 1.
  • Anticipated HbA1c reduction of 3–4 % (e.g., from 13.0 % to ~9.0–10.0 %) over 3–6 months with intensive insulin titration 1.
  • No increase in hypoglycemia incidence when basal‑bolus regimens are correctly implemented versus sliding‑scale monotherapy 1.

Critical Pitfalls to Avoid

  • Never use sliding‑scale insulin as monotherapy in patients requiring insulin—evidence shows it is inferior and unsafe 1.
  • Do not delay prandial insulin addition when pre‑meal glucose consistently exceeds 250 mg/dL and HbA1c > 10 % 1.
  • Avoid basal insulin > 0.5 units/kg/day (61 units for this patient) without concurrent prandial coverage, as this raises hypoglycemia risk without improving control 2, 1.
  • Do not discontinue metformin when starting insulin unless medically contraindicated, to preserve its insulin‑sparing benefits 1.
  • Never give rapid‑acting insulin solely at bedtime as a correction dose, because it markedly increases nocturnal hypoglycemia risk 1.
  • Do not completely withhold basal insulin if the patient becomes NPO, as this can precipitate hyperglycemia and ketosis; reduce the dose by approximately 25 % but continue basal coverage 1.

Hypoglycemia Management

  • Treat any glucose < 70 mg/dL immediately with 15 g of fast‑acting carbohydrate, recheck in 15 minutes, and repeat if needed 2, 1.
  • If hypoglycemia occurs without an obvious precipitant, reduce the implicated insulin dose by 10–20 % promptly 2, 1.
  • Provide comprehensive education on hypoglycemia recognition and treatment, including symptoms, the < 70 mg/dL threshold, and the 15‑g carbohydrate rule 1.

Patient Education Essentials

  • Insulin injection technique and site rotation to prevent lipohypertrophy 1.
  • Hypoglycemia recognition and treatment (symptoms, < 70 mg/dL threshold, 15‑g carbohydrate rule) 1.
  • Sick‑day management: continue insulin even if not eating, check glucose every 4 hours, maintain hydration 1.
  • Glucose monitoring: at least four daily measurements during titration 1.
  • Ketone testing when glucose > 300 mg/dL with nausea/vomiting 1.

Special Considerations for This Patient

  • At BMI 41 kg/m², this patient has severe obesity and insulin resistance, requiring higher insulin doses than typical weight‑based calculations 2, 1.
  • The 10‑year duration of diabetes at age 23 suggests either very early onset type 2 diabetes or possible misclassification of type 1 diabetes; consider checking C‑peptide and autoantibodies if glycemic control remains poor despite aggressive insulin therapy 1.
  • The cellulitis on her back may be contributing to insulin resistance and hyperglycemia; acute infections can increase insulin needs by 40–60 % 1.
  • The anion gap of 17 and bicarbonate of 19 indicate mild metabolic acidosis, likely from ketosis; monitor for resolution with insulin therapy and fluid resuscitation 1.
  • The creatinine of 0.56 and eGFR > 90 indicate normal renal function, so no dose adjustment is needed for renal impairment 1.

References

1
Guideline

Initial Dosing for Lantus (Insulin Glargine) in Patients Requiring Insulin Therapy

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

2
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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