How is the dose of long-acting insulin (e.g. insulin glargine) calculated based on Fasting Blood Sugar (FBS) levels?

Calculating Long-Acting Insulin Dose Based on Fasting Blood Sugar

Start with 10 units once daily or 0.1-0.2 units/kg/day of long-acting insulin (such as insulin glargine), then titrate by 2-4 units every 3 days based on fasting blood glucose levels until reaching target FBS of 80-130 mg/dL. 1, 2

Initial Dosing Algorithm

Standard Starting Dose

• For insulin-naive patients with type 2 diabetes: Begin with 10 units once daily OR 0.1-0.2 units/kg body weight per day, administered at the same time each day 1, 3, 2
• For patients with severe hyperglycemia (blood glucose ≥300 mg/dL or A1C ≥9%): Consider higher starting doses of 0.3-0.4 units/kg/day 2, 4
• Continue metformin and possibly one additional oral agent when initiating basal insulin 1, 4

Example Calculation

For a 70 kg patient:

• Conservative approach: 10 units once daily 2, 4
• Weight-based approach: 70 kg × 0.1-0.2 units/kg = 7-14 units once daily 1, 2

FBS-Based Titration Protocol

Evidence-Based Adjustment Schedule

Adjust dose every 3 days based on fasting blood glucose readings: 1, 2, 4

• If FBS ≥180 mg/dL: Increase by 4 units 2, 4
• If FBS 140-179 mg/dL: Increase by 2 units 2, 4
• If FBS 80-130 mg/dL: Maintain current dose (target achieved) 1, 2
• If FBS <80 mg/dL (especially if <2 readings/week): Decrease by 2 units 4
• If hypoglycemia occurs: Reduce dose by 10-20% immediately 2, 4

Target Goals

• Fasting plasma glucose target: 80-130 mg/dL (4.4-7.2 mmol/L) 1, 2, 4
• Alternative target for some patients: <100 mg/dL (5.5 mmol/L) 5, 6

Patient-Managed vs. Clinic-Managed Titration

The AT.LANTUS study demonstrated that patient self-titration (increasing by 2 units every 3 days when FBS remains above target) achieved greater A1C reductions (-1.22% vs -1.08%) compared to clinic-managed titration, though with slightly higher hypoglycemia rates (33.3% vs 29.8%) 5. Equipping patients with self-titration algorithms based on home glucose monitoring significantly improves glycemic control. 1, 2

Critical Threshold: Recognizing Overbasalization

Stop escalating basal insulin when the dose exceeds 0.5 units/kg/day and consider adding prandial insulin or a GLP-1 receptor agonist instead. 1, 2, 4

Warning Signs of Overbasalization

• Basal insulin dose >0.5 units/kg/day 1, 4
• High bedtime-to-morning glucose differential (≥50 mg/dL) 1, 4
• Hypoglycemia episodes 1, 4
• High glucose variability 1
• Fasting glucose controlled but A1C remains elevated 2, 4

When Basal Insulin Alone Is Insufficient

If A1C remains above goal after 3-6 months of optimized basal insulin (with fasting glucose at target), add prandial insulin starting with 4 units before the largest meal or 10% of the basal dose. 1, 2, 4 Alternatively, consider adding a GLP-1 receptor agonist to minimize hypoglycemia and weight gain risks. 1, 2

Common Pitfalls to Avoid

• Delaying dose titration: Adjust every 3 days during active titration phase; waiting longer unnecessarily prolongs time to glycemic targets 2, 4
• Continuing to escalate basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia leads to suboptimal control and increased hypoglycemia risk 1, 2, 4
• Discontinuing metformin: Continue metformin when adding or intensifying insulin therapy unless contraindicated 1, 2, 4
• Using basal insulin to address postprandial hyperglycemia: Basal insulin controls fasting and between-meal glucose; prandial insulin is needed for meal-related excursions 1, 4

Monitoring Requirements

• Daily fasting blood glucose monitoring is essential during the titration phase 2, 4, 5
• Assess adequacy of insulin dose at every clinical visit, looking specifically for signs of overbasalization 2, 4
• Reassess after 3-6 months to determine if additional therapy is needed 1, 2