A 60-year-old man with Wolff-Parkinson-White syndrome currently receiving pharmacologic treatment presents to the clinic with fatigue and a 2.3-kg (5-lb) weight gain over the past 3 months. Physical examination results are normal. Laboratory tests show:
Na+: 136 mEq/L
K+: 3.8 mEq/L
Cl-: 100 mEq/L
HCO3-: 24 mEq/L
Blood urea nitrogen: 12 mg/dL
Creatinine: 1.1 mg/dL
WBC: 7,000/mm3
Platelet count: 270,000/mm3
Hematocrit: 44%
Hemoglobin: 15.6 g/dL
Thyroid-stimulating hormone: 23 U/mL
Thyroxine: 2.0 μg/dL
Prothrombin time: 12 sec
Activated partial thromboplastin time: 30 sec
The patient did not bring a list of his current medications. Which medication is most likely the cause of his condition?
(A) Amiodarone
(B) Enoxaparin
© Metoprolol
(D) Quinidine
(E) Warfarin