What are the recommended doses of Metformin (metformin) and Januvia (sitagliptin) for a patient with moderate to severe impaired renal function, specifically an estimated Glomerular Filtration Rate (eGFR) of 37?

Dosing Metformin and Januvia with eGFR 37

For a patient with eGFR 37 mL/min/1.73 m², metformin should be reduced to half the maximum dose (typically 1000 mg daily maximum, starting at 500 mg daily), and sitagliptin (Januvia) should be reduced to 25 mg once daily. 1, 2

Metformin Dosing at eGFR 37

Your patient falls into the eGFR 30-44 mL/min/1.73 m² category, which requires specific dose reduction:

• Reduce metformin to 50% of the maximum dose - this typically means a maximum of 1000 mg daily total, often given as 500 mg twice daily or 500 mg once daily initially 1, 3, 4
• Start with 500 mg once daily with meals if initiating therapy, or reduce current dose by half if already on metformin 1, 5
• Monitor renal function every 3-6 months at this eGFR level, as the patient is approaching the threshold where metformin must be discontinued 1, 3, 2
• Discontinue metformin immediately if eGFR falls below 30 mL/min/1.73 m² due to substantially increased risk of lactic acidosis 1, 2

Critical Safety Measures for Metformin at This eGFR

• Educate the patient on "sick day rules" - temporarily stop metformin during any acute illness, dehydration, or before procedures that could precipitate acute kidney injury 3, 2
• Hold metformin before any iodinated contrast procedures and restart only after confirming stable renal function 48 hours post-procedure 2
• Monitor vitamin B12 levels if the patient has been on metformin for more than 4 years 1, 3, 5

Sitagliptin (Januvia) Dosing at eGFR 37

Sitagliptin requires dose reduction to 25 mg once daily for patients with eGFR 30-44 mL/min/1.73 m² 1

• The standard dose of sitagliptin is 100 mg daily, but this must be reduced by 75% at this level of renal function 1
• No further titration is needed - 25 mg once daily is the appropriate maintenance dose 1
• Sitagliptin can be safely used at this eGFR with appropriate dose adjustment, unlike metformin which is approaching its contraindication threshold 1

Important Interaction Consideration

• Do not combine sitagliptin with GLP-1 receptor agonists (such as dulaglutide, semaglutide, or liraglutide) as they work through similar mechanisms and should not be used together 1
• The risk of hypoglycemia with sitagliptin alone is low, but increases if combined with sulfonylureas or insulin - consider reducing doses of these agents if used concomitantly 1

Clinical Pitfalls to Avoid

• Do not use standard metformin dosing at eGFR 37 - this is the most common prescribing error and significantly increases lactic acidosis risk 1, 2
• Do not continue metformin if eGFR drops below 30 - this is an absolute contraindication 1, 2
• Do not use the standard 100 mg dose of sitagliptin - dose reduction is mandatory at this eGFR level 1
• Avoid initiating metformin if eGFR is between 30-45 mL/min/1.73 m² (though continuation with dose reduction is acceptable if already established) 2

Alternative Considerations

Given that this patient is close to the eGFR threshold where metformin must be discontinued, consider discussing with the patient about transitioning to alternative agents:

• GLP-1 receptor agonists (dulaglutide, semaglutide, liraglutide) require no dose adjustment at this eGFR and have cardiovascular benefits 1
• SGLT2 inhibitors can be used if eGFR >20-25 mL/min/1.73 m² depending on the specific agent, and provide cardiovascular and renal protection 1
• These agents may be preferable as add-on therapy rather than increasing metformin dose, given the proximity to the eGFR 30 threshold 1, 3