Management of Hypoglycemia in a Patient on Metformin, Farxiga, and Lantus with eGFR 40
Reduce Lantus by 20% (from 30 units to 24 units daily) and decrease metformin to 1000 mg daily (500 mg twice daily) given the eGFR of 40 mL/min/1.73 m².
Insulin Dose Reduction
The primary cause of hypoglycemia is the addition of Farxiga (dapagliflozin) to an existing insulin regimen without appropriate insulin dose adjustment. The American College of Cardiology guidelines explicitly recommend reducing total daily insulin dose by 20% when initiating SGLT2 inhibitors in patients already on insulin to prevent hypoglycemia 1.
- Reduce Lantus from 30 units to 24 units daily as the initial adjustment 1
- Avoid substantial initial reductions greater than 20%, as this can lead to other complications 1
- Monitor blood glucose closely for 3-4 weeks after this adjustment 1
Metformin Dose Adjustment for Renal Impairment
With an eGFR of 40 mL/min/1.73 m², metformin must be reduced to prevent accumulation and lactic acidosis risk. The current dose of 2000 mg daily (1000 mg twice daily) exceeds safe limits for this level of renal function.
- Reduce metformin to 1000 mg daily total (500 mg twice daily), which represents the maximum recommended dose for eGFR 30-44 mL/min/1.73 m² 2, 3
- This represents a 50% dose reduction from the current regimen 2
- The ADA and KDIGO guidelines specifically recommend this dose reduction at this eGFR level to prevent metformin accumulation 2
Farxiga Continuation and Monitoring
Continue Farxiga at the current dose, as it provides cardiovascular and renal protection independent of glycemic control. The FDA label indicates that dapagliflozin can be used for non-glycemic indications (cardiovascular and renal protection) down to an eGFR of 25 mL/min/1.73 m² 4.
- Farxiga is appropriate at eGFR 40 mL/min/1.73 m² for renal and cardiovascular protection 4
- While not recommended to initiate for glycemic control below eGFR 45 mL/min/1.73 m², it can be continued if already started 4
- Monitor renal function every 3-6 months given eGFR <60 mL/min/1.73 m² 2, 5
Blood Glucose Monitoring Protocol
Implement intensive self-monitoring of blood glucose for the next 3-4 weeks to assess response to dose adjustments and prevent further hypoglycemia.
- Check fasting glucose daily and adjust Lantus based on patterns: if >50% of fasting values exceed 150 mg/dL, increase by 2 units; if >2 values/week are <80 mg/dL, decrease by 2 units 1
- Monitor pre-meal glucose before lunch and dinner to assess overall glycemic control 1
- Target fasting glucose of 90-150 mg/dL (5.0-8.3 mmol/L) 1
Additional Monitoring Requirements
Monitor renal function and vitamin B12 levels given the clinical context.
- Assess eGFR every 3-6 months due to baseline eGFR <60 mL/min/1.73 m² 2, 5
- Check vitamin B12 levels if metformin use exceeds 4 years 1, 5
- Monitor for volume depletion signs (orthostatic lightheadedness) given SGLT2 inhibitor diuretic effects 1
Critical Thresholds for Future Adjustments
Be prepared to make further medication changes if renal function declines.
- If eGFR falls below 30 mL/min/1.73 m², discontinue metformin entirely 2
- If eGFR falls below 25 mL/min/1.73 m² and Farxiga was initiated for glycemic control, consider discontinuation; however, if continued for cardiovascular/renal protection, it may be maintained 4
- Consider adding a GLP-1 receptor agonist if additional glycemic control is needed and eGFR remains >30 mL/min/1.73 m² 3
Common Pitfalls to Avoid
Do not make the mistake of discontinuing Farxiga due to hypoglycemia—the issue is failure to reduce insulin dose proactively, not the SGLT2 inhibitor itself 1. The ACC guidelines emphasize that substantial initial insulin reductions (>20%) should be avoided, but a 20% reduction is both necessary and safe 1. Additionally, do not continue metformin at 2000 mg daily with eGFR 40 mL/min/1.73 m², as this significantly increases lactic acidosis risk 2.