No, Long-Acting Insulin Should Not Be Split Based on Reaching 32 Units
There is no evidence-based threshold of 32 units (or any specific unit amount) that mandates splitting long-acting insulin doses. The decision to split basal insulin is based on inadequate 24-hour coverage or specific glycemic patterns, not on reaching a particular dose number 1.
When to Consider Splitting Long-Acting Insulin
The American Diabetes Association explicitly recognizes that insulin glargine may require twice-daily dosing when once-daily administration fails to provide 24-hour coverage, particularly for:
- Type 1 diabetes patients with persistent glycemic variability despite optimal once-daily dosing 2
- Inadequate 24-hour coverage demonstrated by morning hyperglycemia despite appropriate evening dosing 2
- Persistent nocturnal hypoglycemia with morning hyperglycemia (dawn phenomenon not controlled by timing adjustments) 2
- Patients requiring very high basal insulin doses where absorption capacity may be exceeded with single daily injection 2
The Critical Threshold: 0.5 Units/kg/day
When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, the priority should be adding prandial insulin or GLP-1 receptor agonist rather than continuing to escalate or split basal insulin alone 1. This threshold addresses the phenomenon of "overbasalization" where excessive basal insulin masks insufficient mealtime coverage 1.
Clinical Signals of Overbasalization Include:
- Basal insulin dose >0.5 units/kg/day 1
- Bedtime-to-morning glucose differential ≥50 mg/dL 1
- Hypoglycemia episodes 1
- High glucose variability 1
Standard Dosing Approach
Initial Dosing
- Type 2 diabetes: Start with 10 units once daily or 0.1-0.2 units/kg/day 1
- Type 1 diabetes: Approximately 0.5 units/kg/day as total daily dose, with 40-60% as basal insulin 1
Titration Algorithm
- Increase by 2 units every 3 days if fasting glucose is 140-179 mg/dL 1
- Increase by 4 units every 3 days if fasting glucose ≥180 mg/dL 1
- Target fasting plasma glucose: 80-130 mg/dL 1
Common Pitfalls to Avoid
Do not split basal insulin simply because the dose seems "high" numerically 1. A 70 kg patient could appropriately receive 35 units once daily (0.5 units/kg/day) without needing to split the dose 1.
Once-daily dosing remains the standard initial approach for glargine, with twice-daily dosing reserved for patients who fail to achieve targets or experience problematic hypoglycemia with optimized once-daily regimens 2.
Before implementing twice-daily glargine, ensure proper once-daily dose titration has been attempted and consider whether switching to newer ultra-long-acting insulins (like degludec) might provide more stable 24-hour coverage 2.
Clinical Evidence
Research demonstrates that insulin glargine can be effectively administered as a single daily dose, in the morning, evening, or split between both, with similar glycemic control achieved across all three approaches 3. However, splitting the glargine dose did not offer any advantages in glycemic control parameters in a study of 292 intensively treated type 1 diabetes patients 3.
The pharmacokinetic properties of long-acting basal insulins allow for appropriate steady-state accumulation when dosed once daily at appropriate intervals (every 24 hours), without unwanted insulin stacking 4.