A 42-year-old man with a history of gallstones presents with acute onset epigastric pain, nausea, and vomiting. Serum amylase is elevated at 800 U/L. Abdominal ultrasound confirms acute pancreatitis secondary to choledocholithiasis. After initial fluid resuscitation and supportive care, which antibiotic is the drug of choice for prophylaxis in this patient with predicted severe acute pancreatitis (APACHE score 8)?