A 33-year-old woman was admitted to the hospital because of anorexia, malaise, jaundice, and right upper quadrant abdominal pain for the past 2 days. The woman, who was 2 months' pregnant, was diagnosed with hyperthyroidism 1 month ago and started an appropriate therapy. Pertinent lab results on admission included alanine aminotransferase of 410 U/L (normal 20-40 U/L). Which of the following drugs most likely caused the patient's disorder?