A client is prescribed metformin for type 2 diabetes. Which instruction is MOST important to include in patient teaching?

METFORMIN PATIENT TEACHING PRIORITIES: WITH FOOD: Taking with meals significantly reduces GI side effects (nausea, diarrhea, abdominal discomfort) that cause many patients to discontinue; LACTIC ACIDOSIS: Rare but serious adverse effect; early symptoms: unusual muscle pain, weakness, difficulty breathing, stomach discomfort, dizziness, unusual sleepiness; risk increased with renal impairment — metformin is contraindicated with eGFR below 30; CONTRAST/SURGERY HOLD: Metformin must be HELD 48 hours before IV contrast (risk of contrast-induced nephropathy with metformin = increased lactic acidosis risk) and any major surgery; resume after renal function confirmed normal 48 hours post-procedure; HYPOGLYCEMIA: Metformin alone does NOT cause hypoglycemia (it reduces hepatic glucose production without stimulating insulin release) — this distinguishes it from sulfonylureas; MONITORING: BMP/CMP for renal function monitoring; HbA1c every 3-6 months.