Can I switch an adult patient from insulin degludec (Tresiba) to insulin glargine (Lantus or Toujeo) and how should the basal dose be adjusted?

Switching from Insulin Degludec to Insulin Glargine

Yes, you can switch an adult patient from insulin degludec (Tresiba) to insulin glargine (Lantus or Toujeo), and the basal dose should typically be maintained at a 1:1 unit conversion without routine adjustment at the time of switch.

Dose Conversion Algorithm

Standard 1:1 Unit-for-Unit Conversion

• Switch degludec to glargine U-100 (Lantus) or glargine U-300 (Toujeo) using the same total daily basal insulin dose without initial adjustment, as clinical trials demonstrate equivalent glycemic control with this approach 1.
• The FDA label for insulin degludec confirms that patients can be switched between long-acting basal insulins on a unit-to-unit basis 1.
• Real-world observational data in 266 patients (172 type 1 diabetes, 94 type 2 diabetes) switching from glargine/detemir to degludec showed that the reverse conversion (degludec back to glargine) would follow similar principles 2.

Expected Dose Adjustments After Switch

• For patients previously on degludec once daily, maintain the same dose when switching to glargine U-100 once daily 3, 4.
• A retrospective study of 95 patients switching from glargine U-100 to glargine U-300 showed median dose increases from 30 units to 34.5 units over follow-up (p=0.01), suggesting that when switching from glargine U-300 to degludec, you might expect slightly lower dose requirements 3.
• When switching from degludec to glargine U-100, no significant dose adjustment is typically needed at the time of switch, but monitor closely and titrate based on fasting glucose over the subsequent 1-2 weeks 3, 4.

Timing and Administration

Injection Timing

• Administer glargine U-100 (Lantus) once daily at the same time each day, preferably at bedtime (20:00 h) to align with standard clinical practice 5.
• Glargine U-300 (Toujeo) should also be given once daily at the same time, though it has a flatter pharmacokinetic profile than glargine U-100 3.
• The switch can be made on the day the next degludec dose would have been due—simply substitute glargine at the equivalent dose 1, 4.

Transition Protocol

• On the day of switch, give the first dose of glargine at the same total daily units as the previous degludec dose 1, 3.
• Continue all prandial insulin and oral antidiabetic medications unchanged during the transition period 1, 4.
• Monitor fasting glucose daily for the first 1-2 weeks after switching to guide any necessary dose adjustments 5, 3.

Post-Switch Titration

Basal Insulin Titration After Switch

• Increase glargine by 2 units every 3 days if fasting glucose is 140-179 mg/dL 5.
• Increase glargine by 4 units every 3 days if fasting glucose is ≥180 mg/dL 5.
• Target fasting glucose 80-130 mg/dL 5.
• If hypoglycemia occurs (glucose <70 mg/dL), reduce the dose by 10-20% immediately 5.

Monitoring Requirements

• Check fasting glucose daily during the first 2-3 weeks after switching to assess adequacy of basal coverage 5, 3.
• Reassess HbA1c at 3 months to confirm maintained glycemic control 5.
• Monitor for changes in hypoglycemia patterns, as degludec has been shown to reduce nocturnal hypoglycemia compared to glargine U-100 in some populations 6, 7.

Special Considerations

Type 1 Diabetes Patients

• In type 1 diabetes, switching from degludec to glargine typically requires no initial dose adjustment, but closer monitoring is warranted due to absolute insulin dependence 2, 4.
• A study of 16 type 1 diabetes patients switching to degludec showed that those previously on glargine once daily could switch without down-titration, suggesting the reverse (degludec to glargine) follows similar principles 4.
• Maintain the same prandial insulin doses (approximately 50-60% of total daily insulin) when switching basal insulins 5, 2.

Type 2 Diabetes Patients

• In type 2 diabetes, the 1:1 conversion from degludec to glargine is appropriate, with subsequent titration based on fasting glucose 2, 3.
• Continue metformin at maximum tolerated dose (up to 2000-2550 mg daily) throughout the switch to maintain insulin-sparing effects 5.
• When basal insulin approaches 0.5-1.0 units/kg/day without achieving targets, consider adding prandial insulin or a GLP-1 receptor agonist rather than further basal escalation 5.

Switching to Glargine U-300 (Toujeo) Specifically

• When switching from degludec to glargine U-300, use the same total daily dose initially, but be prepared for potential dose increases of approximately 10-15% over subsequent weeks based on fasting glucose patterns 3.
• Glargine U-300 has a more prolonged and flatter pharmacokinetic profile than glargine U-100, which may provide more stable coverage but could require slightly higher doses 3.

Expected Clinical Outcomes

Glycemic Control

• HbA1c should remain stable when switching from degludec to glargine with appropriate dose conversion and titration 1, 4, 7.
• A 52-week trial comparing degludec to glargine U-100 showed similar HbA1c reductions (estimated treatment difference 0.08% [95% CI: -0.05%; 0.21%]), confirming equivalent efficacy 1.
• Time in range (3.9-10.0 mmol/L) may be slightly lower with glargine U-100 compared to degludec (70.7% vs 72.1%, difference of 20.6 minutes/day), though this difference is clinically modest 6.

Hypoglycemia Risk

• Nocturnal hypoglycemia rates may increase slightly when switching from degludec to glargine U-100, as degludec has demonstrated lower nocturnal hypoglycemia in head-to-head trials 6, 7.
• In the BEGIN Once Long trial, nocturnal confirmed hypoglycemia occurred at 0.25 episodes/patient-year with degludec versus 0.39 episodes/patient-year with glargine U-100 (p=0.038) 7.
• Monitor closely for hypoglycemia during the first 2-4 weeks after switching, particularly overnight 6, 7.

Common Pitfalls to Avoid

Dose Conversion Errors

• Do not routinely reduce the dose by 20-30% when switching from degludec to glargine, as this is not supported by clinical evidence and will lead to inadequate basal coverage 1, 3, 4.
• Do not increase the dose empirically at the time of switch—use a 1:1 conversion and titrate based on fasting glucose over subsequent days 3, 4.
• Avoid switching patients with frequent hypoglycemia from degludec to glargine without careful consideration, as degludec provides more consistent day-to-day absorption and lower nocturnal hypoglycemia risk 6, 7.

Monitoring Failures

• Do not delay dose adjustments if fasting glucose remains >180 mg/dL after switching—titrate aggressively by 4 units every 3 days until target is achieved 5.
• Never discontinue basal insulin entirely in type 1 diabetes, even temporarily during a switch, to prevent diabetic ketoacidosis 5.
• Do not rely solely on correction insulin after switching—ensure adequate scheduled basal coverage is established 5.

Timing and Administration Issues

• Do not switch patients from degludec (which can be given at any time) to glargine without establishing a consistent daily injection time, as glargine requires same-time-each-day dosing for optimal effect 5, 1.
• Avoid giving glargine at bedtime as a sole correction dose—it must be given as scheduled basal insulin 5.

Alternative: When NOT to Switch

Clinical Scenarios Favoring Degludec Retention

• Patients with recurrent nocturnal hypoglycemia should remain on degludec rather than switching to glargine, as degludec provides superior nocturnal glycemic stability 6, 7.
• Patients requiring flexible dosing schedules (e.g., shift workers) benefit from degludec's ultra-long duration of action and can dose at varying times, which is not possible with glargine 1.
• Patients with high day-to-day variability in insulin requirements may achieve better control with degludec due to its more consistent absorption profile 6.