In an adult with type 2 diabetes, A1C 10.9 %, BMI 41, weight 123 kg, currently taking basal insulin glargine (Lantus) 50 U daily, what should the basal dose, carbohydrate‑to‑insulin ratio, and correction factor be?

Insulin Dosing for Severe Uncontrolled Type 2 Diabetes with Obesity

This patient requires immediate basal-bolus insulin therapy with Lantus 60 units once daily at bedtime plus 10–12 units of rapid-acting insulin before each of the three largest meals, while continuing metformin at maximum tolerated dose.

Critical Assessment of Current Regimen

• Lantus 50 units is profoundly inadequate for a 123 kg patient with A1C 10.9%, representing only 0.41 units/kg/day when guidelines recommend 0.5–1.0 units/kg/day for severe hyperglycemia 1.
• The absence of prandial insulin explains persistent hyperglycemia despite basal coverage; basal insulin alone cannot address postprandial glucose excursions when A1C exceeds 9% 1, 2.
• Sliding-scale insulin as monotherapy is condemned by all major diabetes guidelines—only 38% of patients achieve mean glucose <140 mg/dL with sliding-scale alone versus 68% with scheduled basal-bolus therapy 1, 2.

Immediate Basal Insulin Adjustment

Lantus Dose Calculation

• Increase Lantus to 60 units once daily (approximately 0.49 units/kg for 123 kg) administered at bedtime 1, 2.
• This represents the critical threshold of 0.5 units/kg/day; further basal escalation beyond this point should be avoided without concurrent prandial insulin to prevent "over-basalization" 1, 2.

Basal Titration Protocol

• If fasting glucose 140–179 mg/dL: increase Lantus by 2 units every 3 days 1.
• If fasting glucose ≥180 mg/dL: increase Lantus by 4 units every 3 days 1.
• Target fasting glucose: 80–130 mg/dL 1.
• Stop basal escalation when dose approaches 0.5–1.0 units/kg/day (60–123 units); beyond this threshold, intensify prandial insulin instead 1, 2.

Prandial Insulin Initiation (Rapid-Acting)

Starting Dose

• Begin 10–12 units of rapid-acting insulin (lispro, aspart, or glulisine) before each of the three largest meals 1, 2.
• Administer 0–15 minutes before meals for optimal postprandial control 1.

Prandial Titration Protocol

• Check glucose 2 hours after each meal 1, 2.
• If postprandial glucose >180 mg/dL consistently: increase that meal's dose by 2 units every 3 days 1, 2.
• Target postprandial glucose: <180 mg/dL 1, 2.

Carbohydrate-to-Insulin Ratio (ICR)

Initial Ratio Calculation

• Use the 450 rule for rapid-acting insulin: 450 ÷ total daily insulin dose 1.
• With an estimated total daily dose of 90 units (60 basal + 30 prandial), the ICR = 450 ÷ 90 = 5 grams carbohydrate per 1 unit insulin 1.
• Practical starting ratio: 1 unit per 5–10 grams of carbohydrate, adjusted based on postprandial glucose patterns 1.

ICR Adjustment

• If postprandial glucose consistently >180 mg/dL: tighten the ratio (e.g., from 1:10 to 1:8) 1.
• If postprandial glucose <70 mg/dL: loosen the ratio (e.g., from 1:8 to 1:10) 1.

Correction Factor (Insulin Sensitivity Factor)

Calculation

• Use the 1500 rule for regular insulin or 1700 rule for rapid-acting analogs: 1500 ÷ total daily insulin dose 1.
• With 90 units total daily dose: 1500 ÷ 90 = 17 mg/dL drop per 1 unit insulin 1.
• Practical correction scale:
  • Add 2 units for pre-meal glucose >250 mg/dL 1, 2.
  • Add 4 units for pre-meal glucose >350 mg/dL 1, 2.

Correction Dose Timing

• Administer correction insulin in addition to scheduled prandial doses, not as a replacement 1, 2.
• Never give rapid-acting insulin at bedtime as a sole correction dose—this markedly raises nocturnal hypoglycemia risk 1, 2.

Metformin Optimization

• Increase metformin to at least 1,000 mg twice daily (2,000 mg total) unless contraindicated 1, 2.
• Metformin reduces total insulin requirements by 20–30% and provides superior glycemic control when combined with insulin 1, 2.
• Maximum effective dose is up to 2,550 mg/day 1, 2.
• Never discontinue metformin when initiating or intensifying insulin therapy unless medically contraindicated 1, 2.

Glucose Monitoring Requirements

• Fasting glucose daily to guide basal insulin titration 1, 2.
• Pre-meal glucose before every meal to calculate correction doses 1, 2.
• 2-hour postprandial glucose after each meal to assess prandial adequacy 1, 2.
• Minimum 4 checks per day during intensive titration phase 1, 2.

Expected Clinical Outcomes

• 68% of patients achieve mean glucose <140 mg/dL with basal-bolus therapy versus 38% with sliding-scale alone 1, 2.
• HbA1c reduction of 3–4% (from 10.9% to approximately 7–8%) is achievable within 3–6 months with appropriate intensification 1, 2.
• Correctly implemented basal-bolus regimens do not increase hypoglycemia incidence compared with inadequate sliding-scale approaches 1, 2.

Hypoglycemia Management Protocol

• Treat glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate 1, 2.
• Recheck in 15 minutes and repeat if needed 1.
• If hypoglycemia occurs without obvious cause: reduce the implicated insulin dose by 10–20% immediately 1, 2.

Critical Pitfalls to Avoid

• Do not continue escalating Lantus beyond 0.5–1.0 units/kg/day (60–123 units) without addressing postprandial hyperglycemia—this leads to over-basalization with increased hypoglycemia risk and suboptimal control 1, 2.
• Do not delay prandial insulin addition when A1C is 10.9% and pre-meal glucose consistently exceeds 180 mg/dL 1, 2.
• Do not rely solely on correction insulin without scheduled basal-bolus therapy—this perpetuates inadequate control 1, 2.
• Do not discontinue metformin when starting or intensifying insulin unless contraindicated 1, 2.

Follow-Up Schedule

• Visit 1–2 weeks after regimen change to assess glucose control and medication tolerance 1, 2.
• Monthly visits until HbA1c falls below 9%, then every 3 months 1, 2.
• Urgent endocrinology referral if HbA1c remains >9% with unstable glucose 1, 2.

Patient Education Essentials

• Insulin injection technique and site rotation to prevent lipohypertrophy 1.
• Hypoglycemia recognition and treatment: symptoms, <70 mg/dL threshold, 15-gram carbohydrate rule 1, 2.
• Sick-day management: continue insulin even if not eating, check glucose every 4 hours, maintain hydration 1.
• Ketone testing when glucose >300 mg/dL with nausea/vomiting 1.