Metformin Management Before Arthroscopy in Newly Diagnosed Diabetic Patient
No, do not give metformin before dinner on the day before arthroscopy—metformin must be held on the day of surgery. 1
Timing of Metformin Discontinuation
Hold metformin on the day of surgery, not the evening before. The most recent American Diabetes Association guidelines (2023) explicitly state that metformin should be withheld on the day of surgery for perioperative management. 1 This means:
- The patient CAN take metformin with dinner the evening before surgery (assuming surgery is the next day)
- The patient should NOT take metformin on the morning of surgery
- The patient should NOT take any metformin doses on the actual day of the procedure 1
Rationale for This Approach
The concern with metformin perioperatively relates to:
- Risk of lactic acidosis in the setting of surgical stress, potential hypoperfusion, and NPO status 2
- Metformin's renal clearance (approximately 90% eliminated via renal route within 24 hours, with plasma half-life of 6.2 hours), meaning holding it on the day of surgery provides adequate clearance 2
- The drug does not undergo hepatic metabolism and is excreted unchanged in urine, so timing of discontinuation is predictable 2
Practical Management Algorithm
Evening Before Surgery (Dinner Time):
- Give metformin with dinner as usual if surgery is scheduled for the next day 1
- Ensure patient takes medication with food to minimize gastrointestinal side effects 1
- Verify adequate hydration status 2
Day of Surgery:
- Hold all metformin doses 1
- Hold all other oral hypoglycemic agents on the morning of surgery 1
- Target perioperative blood glucose of 100-180 mg/dL (5.6-10.0 mmol/L) 1
- Monitor blood glucose every 2-4 hours while NPO 1
- Use short- or rapid-acting insulin as needed for hyperglycemia rather than oral agents 1
Special Considerations for Newly Diagnosed Diabetic
Since this is a newly diagnosed diabetic patient, additional perioperative considerations include:
- Verify baseline renal function before any metformin use, as renal impairment is a contraindication 2
- Consider whether A1C optimization is needed if this is elective arthroscopy—target A1C <8% for elective surgery when possible 1
- Assess for undiagnosed diabetic complications (autonomic neuropathy, renal failure, ischemic heart disease) that increase perioperative risk 1
- Educate patient about hypoglycemia risk if metformin is combined with insulin or insulin secretagogues perioperatively 1, 2
Postoperative Resumption
- Resume metformin when patient is eating and drinking normally and renal function is stable 1
- Restart at previous dose with food to minimize GI side effects 1
- Continue glucose monitoring until stable on home regimen 1
Critical Pitfall to Avoid
Do not confuse metformin with SGLT2 inhibitors, which require discontinuation 3-4 days before surgery due to euglycemic ketoacidosis risk. 1 Metformin only needs to be held on the day of surgery itself, making the evening-before dose acceptable.