A 30-year-old man is evaluated in the hospital for hyponatremia and dizziness. He reports a 3-day history of fatigue, headache, and imbalance. The patient has had difficult-to-manage nonlesional epilepsy since age 9 years and has required multiple drugs to maintain a seizure rate of only two or three per month. He has no other significant medical history. Medications are oxcarbazepine, levetiracetam, topiramate, and clonazepam.
On physical examination, mental status is normal. Temperature is 37.3 °C (99.1 °F), blood pressure is 95/60 mm Hg, pulse rate is 100/min, and respiration rate is 14/min. Examination of the eyes reveals end-gaze nystagmus in both directions of gaze; the optic discs are sharp. Gait is ataxic.
Creatinine | 0.7 mg/dL (61.9 µmol/L) |
Electrolytes | |
Sodium | 123 mEq/L (123 mmol/L) |
Potassium | 3.5 mEq/L (3.5 mmol/L) |
Chloride | 90 mEq/L (90 mmol/L) |
Bicarbonate | 23 mEq/L (23 mmol/L) |
Which of the following medications is most likely responsible for this patient's findings?