What is the reason for holding metformin in patients with reduced renal function?

LN is 84 YOM who is in hospital for a back surgery. His height is 5 feet and 4 inches, weight 85 kg and NKDA.

His past medical history includes hypertension, diabetes mellitus, major depression, hypothyroidism and chronic back pain. Post-op day 1, LN’s medication includes Dexamethasone 8mg iv q6h with taper dosing, Ondansetron 4mg iv q6h prn for N/V, Levothyroxine 0.075mg po daily, Lisinopril 10mg po daily, Citalopram 20mg po daily, Docusate sodium / Senna 1 tab po twice a day, Bisacodyl 10mg suppository daily prn for constipation, Famotidine 20mg iv q12hr, Metoclopramide 10mg iv q6h, Metformin 500mg po bid, D51/2NS with 20K at 125mls/hour and Hydromorphone PCA at 0.2mg/hour of basal rate, demand dose 0.1mg. lock­out every 6min, one hour limit 2.2mg/hour. Pertinent morning labs includes serum creatinine 1.4mg/dl, Mg 1.5mg/dl, K 5.0mmol/L, Na 135mmol/L.

What is the reason for holding metformin in patients with reduced renal function?

A. Metformin can cause acute renal failure

B. Metformin can cause lactic acidosis

C. Metformin can build up neurotoxin

D. Metformin can cause hyperglycemia

E. Metformin can cause hyperkalemia

View Answer

Answer: B

Explanation:

Metformin is held in patients with reduced renal function due to an increased risk of lactic acidosis. Metformin has a Boxed Warning for lactic acidosis, which is a rare but serious metabolic complication. Lactic acidosis can occurs due to an accumulation of metformin (5 mcg/mL or more). It is fatal in about 50% of cases. Lactic acidosis has also been reported to occur in those with diabetes who have significant renal function impairment. Lactic acidosis occurs when there are elevated blood lactate levels of 5 mmol/L or more, decreased blood pH, electrolyte disturbances with an increased anion gap, and an increased lactate/pyruvate ratio. Normal lactic acid level <2.0 mmol/L.