Which eGFR formula to monitor when on Metformin, CKD-EPI or MDRD?

From the Guidelines

The CKD-EPI formula should be used to monitor kidney function in patients taking metformin, as it provides more accurate estimates of eGFR across a wider range of kidney function. When monitoring kidney function in patients on metformin, it is crucial to choose the most accurate method to ensure safe and effective treatment. The CKD-EPI formula is preferred over the MDRD formula because it provides a more accurate estimation of eGFR, especially in patients with near-normal kidney function 1. Key considerations for metformin use include:

• Metformin can be used safely in individuals with an eGFR ≥30 mL/min/1.73 m², with lower doses recommended for those with an eGFR between 30-45 mL/min/1.73 m² 1.
• eGFR should be monitored every 3 to 6 months in patients at risk for decline in kidney function, and metformin may need to be temporarily discontinued in certain situations, such as before procedures using iodinated contrast or during hospitalizations 1.
• The CKD-EPI formula incorporates variables such as serum creatinine, age, sex, and race to estimate eGFR, providing a more accurate assessment of kidney function compared to the MDRD formula. Regular monitoring of kidney function using the CKD-EPI formula is essential to minimize the risk of lactic acidosis and ensure the safe use of metformin in patients with type 2 diabetes.

From the Research

eGFR Formulas for Metformin Monitoring

When monitoring patients on Metformin, the choice between CKD-EPI and MDRD eGFR formulas is crucial. The following points highlight the key differences and recommendations:

• Both CKD-EPI and MDRD equations are used to estimate glomerular filtration rate (GFR) in patients with chronic kidney disease (CKD) 2, 3, 4, 5, 6.
• A study published in 2021 found a strong relationship between metformin clearance and estimated kidney function using the MDRD (r2 = 0.717) and CKD-EPI (r2 = 0.735) equations 2.
• Another study from 2013 compared the performance of the CKD-EPI equation with the MDRD Study equation in kidney transplant recipients and found that the MDRD Study equation had a lower bias and better accuracy 4.
• However, a 2021 study found that the CKD-EPI equation had a better correlation with creatinine clearance estimation in CKD patients and healthy subjects compared to the MDRD equation 5.
• A 2015 study examined the potential impact of using eGFR rather than serum creatinine to determine metformin eligibility and found that using eGFR expanded the population of individuals for whom metformin is likely safe 6.

Key Considerations

Some key considerations when choosing between CKD-EPI and MDRD eGFR formulas include:

• The CKD-EPI equation may be more accurate in patients with relatively well-preserved kidney function 4.
• The MDRD equation may be more accurate in patients with advanced CKD 4.
• The choice of equation may depend on the specific patient population and the clinical context 5, 6.

Recommendations

Based on the available evidence, the following recommendations can be made:

• Both CKD-EPI and MDRD equations can be used to estimate eGFR in patients on Metformin 2, 3, 4, 5, 6.
• The choice of equation should be based on the individual patient's characteristics and the clinical context 5, 6.
• Further studies are needed to determine the optimal eGFR formula for monitoring patients on Metformin 2, 3, 4, 5, 6.