Insulin Glargine Dosing in Type 1 Diabetes
For adults with type 1 diabetes, start insulin glargine at approximately 40–50% of a total daily insulin dose of 0.5 units/kg/day, administered once daily at the same time each day, with the remaining 50–60% given as rapid-acting prandial insulin divided across three meals.
Initial Dose Calculation
- Begin with a total daily insulin requirement of 0.5 units/kg/day for metabolically stable adults with type 1 diabetes; the acceptable range is 0.4–1.0 units/kg/day 1, 2, 3.
- Allocate 40–50% of this total to insulin glargine as basal coverage, which translates to approximately 0.2–0.25 units/kg/day 1, 2, 3.
- The remaining 50–60% should be rapid-acting prandial insulin (lispro, aspart, or glulisine) divided among three meals 1, 2, 3.
Practical Example
For a 70 kg adult:
- Total daily dose = 0.5 × 70 = 35 units/day
- Glargine (basal) = 40–50% = 14–18 units once daily
- Prandial insulin = 50–60% = 17–21 units total (≈5–7 units per meal) 1, 2
Administration Guidelines
- Inject glargine subcutaneously once daily at the same time every day—morning, evening, or bedtime, whichever is most convenient 2, 4.
- Preferred injection sites include the abdomen, thigh, deltoid, or buttock; rotate sites within the same region to prevent lipodystrophy 2, 3, 4.
- Use 4-mm pen needles to minimize risk of intramuscular injection, which causes unpredictable absorption and hypoglycemia 2.
- Never dilute or mix glargine with other insulins due to its unique pH formulation 1, 4.
Titration Protocol
- Increase glargine by 2 units every 3 days if fasting glucose is 140–179 mg/dL 1, 2.
- Increase glargine by 4 units every 3 days if fasting glucose is ≥180 mg/dL 1, 2.
- Target fasting glucose range: 80–130 mg/dL 1, 2, 3.
- If unexplained hypoglycemia (<70 mg/dL) occurs, immediately reduce the dose by 10–20% 1, 2.
Critical Dosing Threshold
When basal insulin approaches 0.5–1.0 units/kg/day without achieving glycemic targets, intensify prandial insulin rather than continuing to escalate glargine. This prevents "over-basalization," which increases hypoglycemia risk without improving control 1, 2.
Signs of Over-Basalization
- Basal dose >0.5 units/kg/day 1, 2
- Bedtime-to-morning glucose drop ≥50 mg/dL 1, 2
- Recurrent hypoglycemia episodes 1, 2
- High glucose variability throughout the day 1, 2
Special Populations Requiring Dose Adjustments
- Diabetic ketoacidosis presentation: Use higher weight-based dosing than the standard 0.5 units/kg/day initially 1, 3.
- Puberty: Insulin requirements often approach 1.0 units/kg/day or higher 1, 3.
- Pregnancy: Higher doses are required throughout gestation 1, 3.
- Honeymoon phase: Lower doses of 0.2–0.6 units/kg/day may suffice 1, 3.
- Acute illness or infection: May require doses approaching 1.0 units/kg/day or more 1, 3.
Renal Impairment Adjustments
- For CKD Stage 5, reduce total daily insulin by 35–40% in type 1 diabetes 2.
- Monitor more closely for hypoglycemia as insulin clearance decreases with declining kidney function 2.
- Titrate conservatively when eGFR <45 mL/min/1.73 m² 2.
Hypoglycemia Management
- Treat any glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate, recheck in 15 minutes, and repeat if needed 1, 2.
- All patients must carry at least 15g carbohydrate at all times 2.
- Scrupulous avoidance of hypoglycemia for 2–3 weeks can reverse hypoglycemia unawareness 2.
Common Pitfalls to Avoid
- Never use glargine as monotherapy in type 1 diabetes—it must be combined with rapid-acting prandial insulin to prevent diabetic ketoacidosis 1, 4.
- Avoid intramuscular injection, which causes erratic absorption and frequent hypoglycemia 2.
- Do not inject into areas of lipohypertrophy, as this causes unpredictable absorption 2, 4.
- Never administer glargine intravenously or via an insulin pump 4.