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

METFORMIN (Glucophage) is the FIRST-LINE oral medication for type 2 diabetes. MECHANISM: decreases hepatic glucose production (gluconeogenesis); increases insulin sensitivity in peripheral tissues; mild GI effects slow glucose absorption. CRITICAL PATIENT EDUCATION — CONTRAST DYE: Metformin + iodinated IV contrast can cause LACTIC ACIDOSIS — a rare but potentially fatal complication. PROTOCOL: HOLD METFORMIN before any procedure requiring IV iodinated contrast (CT scans, cardiac catheterization, angiography); restart ONLY after kidney function confirmed adequate (typically 48 hours after procedure with normal serum creatinine). The risk is related to metformin's renal clearance — if contrast causes acute kidney injury, metformin accumulates. LACTIC ACIDOSIS WARNING SIGNS: nausea, vomiting, abdominal pain, fatigue, muscle pain, rapid breathing (Kussmaul respirations), dizziness — report immediately. ADDITIONAL TEACHING POINTS: (1) TAKE WITH FOOD: metformin is taken WITH meals to reduce GI side effects (nausea, diarrhea, abdominal cramping — most common side effects, usually improve over time); (2) DOES NOT CAUSE HYPOGLYCEMIA alone — unlike sulfonylureas and insulin, metformin does not stimulate insulin secretion and does NOT typically cause hypoglycemia when used as monotherapy; (3) HOLD BEFORE SURGERY: general anesthesia and NPO status can affect kidney function; (4) CONTRAINDICATIONS: renal impairment (eGFR <30 mL/min contraindicated; use caution and possibly reduce dose at eGFR 30-45); hepatic impairment; heart failure requiring treatment; (5) SIDE EFFECT — vitamin B12 deficiency with long-term use; periodically check B12. PN ROLE: educate on contrast dye holding; teach to take with food; reinforce hypoglycemia is NOT typically expected from metformin alone; instruct to report unusual fatigue, muscle aches, or breathing difficulty.