Long-Acting Insulin is Used for Fasting Glucose Control
Long-acting insulin like Lantus (insulin glargine) is specifically designed to control fasting and between-meal glucose levels, NOT postprandial (after-meal) glucose. 1, 2
Primary Mechanism and Purpose
- The principal action of basal insulin is to restrain hepatic glucose production and limit hyperglycemia overnight and between meals. 1
- Insulin glargine provides relatively constant basal insulin coverage over 24 hours with no pronounced peak, making it ideal for controlling fasting plasma glucose. 1
- The peakless pharmacokinetic profile means glargine maintains stable blood glucose levels during sleep and between meals, not during the postprandial period. 1, 2
Pharmacological Properties Supporting Fasting Control
- Insulin glargine has an onset of action of approximately 1 hour, with a peakless profile and duration of up to 24 hours. 2
- After subcutaneous injection, glargine forms microprecipitates that slowly release insulin, creating a relatively constant plasma concentration over 24 hours. 3
- This flat time-action profile is specifically designed to mimic endogenous basal insulin secretion, which primarily suppresses hepatic glucose output between meals and overnight. 4
Clinical Application: What Controls Postprandial Glucose?
- Rapid-acting insulin (lispro, aspart, glulisine) controls postprandial blood glucose more effectively than regular insulin. 1
- These rapid-acting insulins should be administered 0-15 minutes before meals to manage postprandial glucose excursions. 5
- In type 1 diabetes, glargine must be combined with rapid-acting insulin at mealtimes to control glucose surges after meals. 6, 7
Critical Clinical Pitfall: Overbasalization
- Attempting to control postprandial hyperglycemia by increasing basal insulin leads to "overbasalization"—a dangerous pattern where excessive basal insulin causes hypoglycemia without adequately addressing meal-related glucose spikes. 2, 5
- Clinical signs of overbasalization include: basal insulin dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia, and high glucose variability. 2, 5
- When basal insulin approaches 0.5-1.0 units/kg/day and fasting glucose is controlled but A1C remains elevated, add prandial insulin rather than continuing to escalate basal insulin. 2, 5
Practical Treatment Algorithm
- For fasting hyperglycemia: Titrate glargine by 2-4 units every 3 days until fasting glucose reaches 80-130 mg/dL. 1, 5
- For postprandial hyperglycemia (despite controlled fasting glucose): Add rapid-acting insulin before meals, starting with 4 units before the largest meal or 10% of basal dose. 2, 5
- Never increase basal insulin beyond 0.5 units/kg/day to address postprandial excursions—this leads to suboptimal control and increased hypoglycemia risk. 2, 5