When to Start Long-Acting Insulin
Start long-acting basal insulin when oral medications and/or GLP-1 receptor agonists fail to achieve glycemic targets (A1C >7% for most adults, <6.5% for youth with type 2 diabetes), or immediately in patients with severe hyperglycemia (A1C ≥9%, blood glucose ≥300-350 mg/dL, or symptomatic/catabolic features). 1
Indications for Initiating Basal Insulin
Type 2 Diabetes - Adults
- A1C >7% despite optimal oral medications (metformin plus additional agents) 1
- A1C ≥9% - consider starting insulin earlier in the treatment algorithm 1
- Blood glucose ≥300-350 mg/dL and/or A1C 10-12% with symptomatic or catabolic features (weight loss, polyuria, polydipsia) - start basal-bolus insulin immediately 1
- Presence of diabetic ketoacidosis or hyperosmolar hyperglycemic state 1
Type 2 Diabetes - Youth
- A1C >8.5% without acidosis or ketosis - start metformin plus long-acting insulin at 0.5 units/kg/day 1
- A1C <8.5% - start metformin alone, add insulin if goals not met 1
- Any presentation with acidosis, DKA, or HHS - start insulin immediately 1
Type 1 Diabetes
- Basal insulin is required from diagnosis as part of a basal-bolus regimen, comprising approximately one-third of total daily insulin requirements 2
How to Start Long-Acting Insulin
Initial Dosing Protocols
Type 2 Diabetes - Insulin-Naive Patients
Starting dose: 10 units once daily OR 0.1-0.2 units/kg/day, administered at the same time each day. 1, 3, 2, 4
- For a typical 70 kg patient: start with 10 units daily 3
- For patients with severe hyperglycemia (A1C ≥9%, glucose ≥300 mg/dL): consider higher starting doses of 0.3-0.4 units/kg/day 3
- Administer subcutaneously into abdomen, thigh, or deltoid; rotate injection sites within the same region 2
Type 2 Diabetes - Youth
Starting dose: 0.5 units/kg/day when A1C >8.5% with no acidosis. 1
- Titrate every 2-3 days based on blood glucose monitoring 1
- If pancreatic autoantibodies are positive, transition to multiple daily injection regimen as for type 1 diabetes 1
Type 1 Diabetes
Starting dose: Approximately one-third of total daily insulin requirements (typically 0.4-1.0 units/kg/day total, with 0.5 units/kg/day being typical for metabolically stable patients). 5, 3, 2
- Use short-acting premeal insulin for the remaining two-thirds of daily requirements 2
- Higher doses needed immediately following ketoacidosis presentation 3
Titration Algorithm
Standard Titration Protocol
Increase dose by 2-4 units (or 10-15%) once or twice weekly until fasting blood glucose reaches 80-130 mg/dL. 1, 3, 4
Specific titration based on fasting glucose: 3
- Fasting glucose ≥180 mg/dL: increase by 4 units every 3 days
- Fasting glucose 140-179 mg/dL: increase by 2 units every 3 days
- Fasting glucose 80-130 mg/dL: maintain current dose
Monitoring During Titration
- Daily fasting blood glucose monitoring is essential during active titration 3
- Reassess every 3 days during active titration 3
- Once stable, reassess every 3-6 months 3
- If hypoglycemia occurs, determine cause and reduce dose by 10-20% 3
Switching from Other Insulins
From NPH Insulin
- Once-daily NPH to once-daily glargine: use same dose 2
- Twice-daily NPH to once-daily glargine: start at 80% of total NPH dose 2
From Insulin Glargine U-300 (Toujeo)
- To glargine U-100 (Lantus): start at 80% of Toujeo dose 2
Critical Pitfalls to Avoid
Overbasalization
Stop escalating basal insulin when dose exceeds 0.5 units/kg/day and A1C remains above target despite controlled fasting glucose. 1, 5, 3
Clinical signals of overbasalization: 5, 3
- Basal dose >0.5 units/kg/day
- High bedtime-to-morning glucose differential (≥50 mg/dL)
- Hypoglycemia episodes
- High glucose variability
When overbasalization is suspected: 1, 3
- Add prandial insulin (start with 4 units or 10% of basal dose before largest meal) rather than continuing to increase basal insulin
- Consider adding GLP-1 receptor agonist to minimize weight gain and hypoglycemia risk 1, 3
Delaying Insulin Therapy
- Do not delay insulin initiation in patients not achieving glycemic goals with oral medications 1, 3
- Timely dose titration is critical - failure to uptitrate leads to prolonged hyperglycemia 1, 3
Administration Errors
- Never dilute or mix insulin glargine with any other insulin or solution due to its low pH 5, 2
- Do not administer intravenously or via insulin pump 2
- Avoid injecting into areas of lipodystrophy or localized cutaneous amyloidosis 2
When to Add Prandial Insulin
Add prandial insulin when: 1, 3
- Basal insulin has been optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months
- Basal insulin dose approaches 0.5-1.0 units/kg/day without achieving A1C goal
- Significant postprandial glucose excursions persist
Starting prandial insulin: 1, 3
- Begin with 4 units of rapid-acting insulin before the largest meal OR 10% of current basal dose
- Add to other meals based on glucose patterns
- Titrate by 1-2 units or 10-15% every 3 days based on pre-meal and 2-hour postprandial readings
Special Populations
Hospitalized Patients
- Insulin-naive or low-dose insulin: start 0.3-0.5 units/kg total daily dose, with half as basal 3
- High-dose home insulin (≥0.6 units/kg/day): reduce total daily dose by 20% to prevent hypoglycemia 3
- High-risk patients (elderly >65 years, renal failure, poor oral intake): use lower doses of 0.1-0.25 units/kg/day 3