How to adjust insulin glargine (Lantus) and carbohydrate ratio when adding metformin (Glucophage) and empagliflozin (Jardiance) to a patient's regimen?

Insulin and Carbohydrate Ratio Adjustment When Adding Metformin and Empagliflozin

Reduce your Lantus dose by 10-20% (approximately 7-13 units, bringing you to 53-59 units daily) when initiating metformin 500 mg twice daily and empagliflozin 10 mg, and maintain your current carbohydrate ratio (1:4) and correction factor (1:15) initially, then titrate based on glucose monitoring over the following 2-3 weeks. 1

Basal Insulin Reduction Strategy

Initial Lantus Adjustment:

• Decrease your current 66 units by 10-20% to account for the additive glucose-lowering effects of metformin and empagliflozin 1
• This translates to a reduction of 7-13 units, bringing your dose to 53-59 units daily 1
• The 10% reduction is more conservative if your current A1C is near goal; use 20% if A1C is significantly elevated 1

Rationale for Reduction:

• Metformin improves glycemic control primarily by reducing hepatic glucose production and postprandial glucose excursions, which will lower your basal insulin requirements 2
• Empagliflozin as add-on to metformin provides additional A1C reduction of approximately 0.7-1.0%, with significant reductions in both fasting and postprandial glucose 3, 4
• The combination of empagliflozin plus metformin reduces HbA1c by 1.9-2.1% in treatment-naive patients, demonstrating substantial glucose-lowering synergy 4

Carbohydrate Ratio and Correction Factor Management

Initial Approach:

• Keep your 1:4 carbohydrate ratio unchanged initially 1
• Maintain your 1:15 insulin sensitivity factor (correction scale) unchanged initially 1
• These ratios should be reassessed after 3-7 days of stable glucose patterns on the new regimen 1

Subsequent Titration:

• Monitor fasting glucose closely; if consistently below target, further reduce Lantus by 2-4 units every 3 days 1
• If postprandial glucose levels improve significantly (which is expected with metformin and empagliflozin), you may need to reduce your mealtime insulin by adjusting your carb ratio from 1:4 to 1:5 or 1:6 over subsequent weeks 2, 4
• Empagliflozin causes weight loss (2.8-3.8 kg expected), which will improve insulin sensitivity and may require further ratio adjustments 4

Monitoring and Safety Considerations

Critical Monitoring Parameters:

• Check fasting glucose daily for the first week to guide Lantus titration 1
• Monitor pre- and post-meal glucose to assess whether carb ratios need adjustment 1
• Hypoglycemia risk is minimal with this combination (only 2% incidence with empagliflozin vs 24% with sulfonylureas), but remain vigilant 3
• Ensure adequate hydration as empagliflozin increases urinary glucose excretion 5

Titration Timeline:

• Reassess basal insulin dose every 3 days based on fasting glucose patterns 1
• Reassess carbohydrate ratios after 1-2 weeks once glucose patterns stabilize 1
• The full glucose-lowering effect of metformin takes approximately 4 months to manifest, so expect gradual improvement 2

Important Caveats

Avoid Over-Reduction:

• Do not reduce insulin too aggressively initially; a 10-20% reduction is evidence-based and safe 1
• If you experience hypoglycemia, reduce the corresponding insulin component (basal or bolus) by an additional 10-20% 1

Weight and Insulin Sensitivity:

• At BMI 30 (95 kg), you will likely experience 3-4 kg weight loss with empagliflozin, which will further improve insulin sensitivity over 3-6 months 4
• This progressive improvement means you should anticipate additional insulin reductions of 10-15% over the subsequent 2-3 months as weight decreases 1

Renal Monitoring:

• Empagliflozin can be safely initiated if your eGFR is >20 mL/min/1.73 m² 1
• Monitor for increased urinary calcium excretion, though this is generally mild 6