In a patient with type 2 diabetes mellitus on insulin glargine (Lantus) 50 units daily, hemoglobin A1c 10.9 % and BMI 41 kg/m², what should the carbohydrate‑to‑insulin ratio and insulin‑sensitivity correction factor be?

Insulin Dosing for Severe Uncontrolled Type 2 Diabetes with Obesity

This patient requires immediate basal-bolus insulin therapy, not just Lantus titration, because an HbA1c of 10.9% with BMI 41 indicates severe insulin resistance that cannot be managed with basal insulin alone.

Immediate Regimen Restructuring Required

Calculate Total Daily Insulin Dose

• For severe hyperglycemia (HbA1c >9%), start with 0.3–0.5 units/kg/day as the total daily insulin requirement 1, 2, 3.
• At BMI 41 and assuming approximate weight of 110–120 kg, this translates to 33–60 units/day total 1.
• Given the HbA1c of 10.9%, use the higher end: approximately 50–60 units/day total 1, 2.

Basal Insulin (Lantus) Dosing

• Allocate 50% of total daily dose to basal insulin → 25–30 units of Lantus once daily (not 50 units) 1, 2, 3.
• The current 50 units of Lantus alone is inappropriate because it represents basal-only therapy when basal-bolus is required 1.
• Administer Lantus at bedtime or the same time daily 2, 3.

Prandial Insulin Initiation (Essential Component)

• Allocate the remaining 50% of total daily dose to prandial insulin → 25–30 units total, divided among three meals 1, 2, 3.
• Start with 8–10 units of rapid-acting insulin (lispro, aspart, or glulisine) before each of the three largest meals 1, 2, 3.
• Administer prandial insulin 0–15 minutes before meals 1, 2.

Correction Insulin Protocol

• Add 2 units of rapid-acting insulin for pre-meal glucose >250 mg/dL 1.
• Add 4 units of rapid-acting insulin for pre-meal glucose >350 mg/dL 1.
• These correction doses are in addition to scheduled prandial insulin 1.

Carbohydrate-to-Insulin Ratio Calculation

Initial Ratio Determination

• Use the 450 rule for rapid-acting insulin analogs: 450 ÷ total daily dose (TDD) 1.
• With an estimated TDD of 50–60 units: 450 ÷ 55 = approximately 1:8 ratio (1 unit per 8 grams of carbohydrate) 1.
• For severe insulin resistance (BMI 41), the ratio may need to be tightened to 1:6 or 1:7 after initial assessment 1.

Practical Application

• If a meal contains 60 grams of carbohydrate and the ratio is 1:8, the patient needs 60 ÷ 8 = 7.5 units (round to 8 units) 1.
• This carbohydrate coverage dose is separate from any correction dose needed for pre-meal hyperglycemia 1.

Insulin Sensitivity Factor (Correction Scale)

Calculate Correction Factor

• Use the 1500 rule for regular insulin or 1700 rule for rapid-acting analogs: 1500 ÷ TDD 1.
• With TDD of 55 units: 1500 ÷ 55 = approximately 27 mg/dL per unit 1.
• This means 1 unit of insulin will lower blood glucose by approximately 27 mg/dL 1.

Correction Dose Calculation

• Correction dose = (Current glucose – Target glucose) ÷ Insulin Sensitivity Factor 1.
• Example: If pre-meal glucose is 250 mg/dL and target is 125 mg/dL: (250 – 125) ÷ 27 = 4.6 units (round to 5 units) 1.
• For simplicity, use the simplified sliding scale: 2 units for glucose >250 mg/dL, 4 units for >350 mg/dL 1.

Titration Protocols

Basal Insulin (Lantus) Titration

• Increase by 4 units every 3 days if fasting glucose is ≥180 mg/dL 1, 2, 3.
• Increase by 2 units every 3 days if fasting glucose is 140–179 mg/dL 1, 2, 3.
• Target fasting glucose 80–130 mg/dL 1, 2, 3.
• Stop escalating basal insulin when dose exceeds 0.5 units/kg/day (approximately 55–60 units for this patient) 1, 2, 3.

Prandial Insulin Titration

• Adjust each meal dose by 1–2 units (or 10–15%) every 3 days based on 2-hour post-prandial glucose 1, 2, 3.
• Target post-prandial glucose <180 mg/dL 1, 2.
• If post-prandial glucose consistently exceeds 180 mg/dL, increase that specific meal's insulin dose 1.

Carbohydrate Ratio Adjustment

• If post-prandial glucose is consistently >180 mg/dL, tighten the ratio (e.g., from 1:8 to 1:7) 1.
• If post-prandial glucose is consistently <70 mg/dL, loosen the ratio (e.g., from 1:8 to 1:10) 1.
• Reassess the ratio every 2–4 weeks during intensive titration 1.

Correction Factor Adjustment

• If correction doses consistently fail to bring glucose into target range, recalculate the insulin sensitivity factor using the updated TDD 1.
• The correction factor should be adjusted independently from basal and prandial doses 1.

Critical Threshold: Preventing Overbasalization

Warning Signs

• Basal insulin dose >0.5 units/kg/day (>55–60 units for this patient) 1, 2, 3.
• Bedtime-to-morning glucose differential ≥50 mg/dL (large overnight glucose drop) 1, 3.
• Recurrent hypoglycemia (glucose <70 mg/dL) 1, 3.
• High glucose variability throughout the day 1, 3.

Action Required

• When these signs appear, stop increasing basal insulin and intensify prandial insulin instead 1, 2, 3.
• Continuing to escalate basal insulin beyond 0.5–1.0 units/kg/day without adequate prandial coverage leads to increased hypoglycemia risk without improved control 1, 2, 3.

Foundation Therapy: Metformin Optimization

Metformin Dosing

• Continue or maximize metformin to 2000 mg daily (1000 mg twice daily with meals) unless contraindicated 1, 2, 3.
• Metformin reduces total insulin requirements by 20–30% and provides superior glycemic control when combined with insulin 1, 2.
• Never discontinue metformin when starting or intensifying insulin unless medically contraindicated 1, 2, 3.

Other Oral Agents

• Discontinue sulfonylureas when initiating basal-bolus insulin to prevent additive hypoglycemia risk 1, 2, 3.
• Consider adding an SGLT2 inhibitor or GLP-1 receptor agonist for complementary mechanisms and cardiovascular benefits 2, 3.

Monitoring Requirements

Daily Glucose Checks

• Fasting glucose daily to guide basal insulin adjustments 1, 2, 3.
• Pre-meal glucose before each meal to calculate correction doses 1.
• 2-hour post-prandial glucose after each meal to assess prandial insulin adequacy 1, 2.
• Bedtime glucose to evaluate overall daily pattern 1.

HbA1c Monitoring

• Check HbA1c every 3 months during intensive titration 1, 2, 3.
• Expected HbA1c reduction of 3–4% over 3–6 months with proper basal-bolus therapy (from 10.9% to approximately 7–8%) 1.

Hypoglycemia Management

Treatment Protocol

• Treat any glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate 1, 2, 3.
• Recheck glucose in 15 minutes and repeat treatment if needed 1, 3.
• If hypoglycemia occurs without clear cause, reduce the implicated insulin dose by 10–20% immediately 1, 2, 3.

Prevention Strategies

• Never administer rapid-acting insulin at bedtime as a sole correction dose because it markedly raises nocturnal hypoglycemia risk 1.
• If >2 fasting glucose values per week are <80 mg/dL, decrease basal insulin by 2 units 1, 3.

Patient Education Essentials

Injection Technique

• Teach proper insulin injection technique and site rotation to prevent lipohypertrophy 1, 2, 3.
• Administer rapid-acting insulin 0–15 minutes before meals for optimal post-prandial control 1, 2.

Self-Management Skills

• Provide training on carbohydrate counting to use the insulin-to-carbohydrate ratio effectively 4, 1.
• Educate on hypoglycemia recognition and treatment (symptoms, <70 mg/dL threshold, 15-gram carbohydrate rule) 1, 2, 3.
• Teach "sick day" management rules: continue insulin even if not eating, check glucose every 4 hours, maintain hydration 1, 3.
• Instruct on glucose monitoring: at least four daily measurements during titration 1, 2, 3.

Expected Clinical Outcomes

Glycemic Control

• With properly implemented basal-bolus therapy, approximately 68% of patients achieve mean glucose <140 mg/dL versus only 38% with inadequate regimens 1.
• Expected HbA1c reduction of 3–4% (from 10.9% to approximately 7–8%) over 3–6 months 1.
• No increase in hypoglycemia incidence when basal-bolus regimens are correctly applied 1.

Weight Considerations

• Expect weight gain of 2–4 kg with insulin intensification, which is mitigated by continuing metformin 1, 2.
• Consider adding a GLP-1 receptor agonist to minimize weight gain while improving glycemic control 2, 3.

Common Pitfalls to Avoid

Regimen Errors

• Do not use basal insulin alone (current 50 units Lantus monotherapy) for HbA1c >9%; basal-bolus therapy is required 1, 2, 3.
• Do not continue escalating basal insulin beyond 0.5–1.0 units/kg/day without addressing post-prandial hyperglycemia 1, 2, 3.
• Do not rely solely on correction insulin without scheduled basal and prandial doses 1.
• Sliding-scale insulin as monotherapy is condemned by all major diabetes guidelines and shown to be ineffective 1.

Medication Management

• Do not discontinue metformin when starting insulin unless contraindicated 1, 2, 3.
• Do not delay insulin intensification in patients not achieving glycemic goals 1, 2, 3.

Monitoring Failures

• Do not delay dose adjustments when glucose patterns indicate inadequate coverage 1.
• Do not ignore signs of overbasalization (basal dose >0.5 units/kg/day, large overnight glucose drops, hypoglycemia) 1, 3.