Is the dose of Lantus (insulin glargine U‑100) interchangeable with Toujeo (insulin glargine U‑300)?

Lantus and Toujeo Doses Are NOT Interchangeable

When switching from Lantus (insulin glargine U-100) to Toujeo (insulin glargine U-300), you must reduce the Lantus dose by 20% to calculate the starting Toujeo dose; conversely, when switching from Toujeo to Lantus, use 80% of the Toujeo dose as your starting Lantus dose. 1

Why the Doses Differ

The two formulations are not bioequivalent despite containing the same insulin molecule 2, 3:

• Toujeo requires 10-18% higher daily doses than Lantus to achieve equivalent glycemic control due to modestly lower per-unit efficacy 2, 3
• The threefold higher concentration (U-300 vs U-100) creates a smaller subcutaneous depot that releases insulin more slowly, resulting in flatter and more prolonged pharmacokinetics 4, 5
• Steady-state M1 metabolite (the active form) is achieved after 2 days with Lantus but takes 4 days with Toujeo 6

Specific Conversion Protocol

Switching from Toujeo to Lantus:

• Start with 80% of the Toujeo dose 1
• Example: Patient on 100 units Toujeo → start 80 units Lantus
• This FDA-mandated reduction prevents hypoglycemia during the transition 1

Switching from Lantus to Toujeo:

• Increase the dose by approximately 10-18% 2
• Example: Patient on 66 units Lantus → start 73-78 units Toujeo
• The higher dose compensates for Toujeo's lower per-unit potency 2

Clinical Advantages of Toujeo Over Lantus

Toujeo demonstrates superior hypoglycemia safety in head-to-head trials 2:

• Significantly lower rates of clinically significant hypoglycemia (<54 mg/dL): 0% vs 6.0% (p=0.023) 2
• Reduced nocturnal hypoglycemia episodes, particularly in insulin-experienced type 2 diabetes patients 5, 7
• More predictable timing of nocturnal hypoglycemia when it does occur 7

Duration of action exceeds 24 hours with Toujeo, providing more stable basal coverage and reduced glucose variability compared to Lantus's approximately 24-hour duration 2, 3, 5

Reduced injection volume for patients requiring large doses (e.g., 100 units = 0.33 mL with Toujeo vs 1.0 mL with Lantus), improving comfort and adherence 2, 3

When to Switch from Lantus to Toujeo

Switch patients experiencing recurrent nocturnal hypoglycemia on Lantus to Toujeo for superior hypoglycemia safety 2

Switch patients with significant glucose variability who may benefit from Toujeo's longer, flatter action profile 2

Do not switch patients achieving target control without hypoglycemia on Lantus, as they do not require Toujeo's advantages 2

Critical Monitoring Requirements

• Increase blood glucose monitoring frequency during any insulin formulation switch 1
• Close medical supervision is mandatory when changing between glargine formulations 2
• Titrate based on fasting glucose patterns over the first 1-2 weeks after switching 2

Common Pitfall to Avoid

Never assume unit-for-unit equivalence between Lantus and Toujeo—this is the most dangerous error in clinical practice 2, 1. The FDA label explicitly warns that switching between formulations requires dose adjustment under medical supervision 1.

Before escalating either glargine formulation beyond 0.5 units/kg/day with A1C still above target, consider adding GLP-1 receptor agonists or prandial insulin rather than continuing to increase basal insulin alone 2. Signs of overbasalization include bedtime-to-morning glucose differential ≥50 mg/dL and increased hypoglycemia 2.