You are answering a USMLE-style medical question. Question: A 66-year-old man presents to the emergency department with abdominal pain, nausea, and vomiting. He endorses diffuse abdominal tenderness. His past medical history is notable for diabetic nephropathy, hypertension, dyslipidemia, depression, and morbid obesity. He also is currently being treated for an outbreak of genital herpes. His temperature is 99.0°F (37.2°C), blood pressure is 184/102 mmHg, pulse is 89/min, respirations are 18/min, and oxygen saturation is 98% on room air. Physical exam is notable for an obese man in no acute distress. A CT scan of the abdomen with contrast is performed and is unremarkable. The patient is admitted to the observation unit for monitoring of his pain. Notably, the patient's abdominal pain improves after an enema and multiple bowel movements. The patient's evening laboratory values are ordered and return as seen below. Serum: Na+: 141 mEq/L Cl-: 99 mEq/L K+: 4.8 mEq/L HCO3-: 11 mEq/L BUN: 20 mg/dL Glucose: 177 mg/dL Creatinine: 3.1 mg/dL Which of the following is the most likely etiology of this patient's laboratory derangements? Options: A) Acyclovir B) Atorvastatin C) Metformin D) Metoprolol Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.