CNS Pharmacology USMLE Step 1 Practice Question

A 52-year-old obese man presents to his primary care physician after routine bloodwork revealed a fasting glucose of 187 mg/dL and a hemoglobin A1c of 8.2%. He has a BMI of 34 kg/m² and a blood pressure of 138/86 mmHg. Physical examination reveals acanthosis nigricans along the posterior neck and axillae, consistent with insulin resistance. His serum creatinine is 0.9 mg/dL and his eGFR is 88 mL/min/1.73m². He is diagnosed with type 2 diabetes mellitus and started on first-line oral pharmacotherapy that works by lowering hepatic gluconeogenesis and improving peripheral insulin sensitivity. He asks his physician about a serious but rare toxicity associated with this medication that is more likely to occur in the setting of renal failure. Which of the following drugs is most likely being discussed?