Review Question - QID 214495

A 33-year-old homeless man is brought into the emergency department after having a seizure. The patient has a known seizure disorder but has not been following up with his neurologist for the past year nor does he take his medications regularly. His temperature is 99.2°F (37.3°C), blood pressure is 137/92 mmHg, pulse is 93/min, respirations are 16/min, and oxygen saturation is 100% on room air. A chest radiograph and head CT are performed and are negative. Urine is collected for urinalysis. While in the emergency department, the patient has a prolonged seizure and is given multiple doses of lorazepam, a loading dose of phenytoin, and then is started on standing IV phenytoin. His seizure activity improves with these measures and he is admitted to the neurology intensive care unit. While on the unit, his blood pressure is 97/52 mmHg, pulse is 43/min, respirations are 10/min, and oxygen saturation is 95% on room air. Laboratory studies are ordered as seen below.

Serum:
Na+: 142 mEq/L
Cl-: 101 mEq/L
K+: 3.9 mEq/L
HCO3-: 10 mEq/L
BUN: 22 mg/dL
Glucose: 111 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL

The patient’s urine culture returns negative. Which of the following is the most likely etiology of this patient’s symptoms while on the neurology floor?