A 28-year-old woman with bipolar I disorder has been stable on lithium 900 mg daily for 6 months. Three days ago, she developed acute gastroenteritis with persistent vomiting and diarrhea. Despite severe fluid losses, she continued taking her lithium without supplemental fluid intake. She now presents to the emergency department complaining of confusion and difficulty with coordination. On examination, she has a coarse tremor at rest, is disoriented to time and place, and has ataxia. Vital signs show temperature 37.2°C, blood pressure 98/62 mmHg, heart rate 112 beats/min, and respiratory rate 20 breaths/min. Serum lithium level is 3.2 mEq/L (therapeutic range 0.6–1.2 mEq/L), serum creatinine is 2.8 mg/dL (baseline 0.9 mg/dL), serum sodium is 149 mEq/L, and urine output is decreased. Which of the following is the most appropriate initial management?

1. A)Aggressive normal saline rehydration and hemodialysis consultation for levels >3 mEq/LGABARITO
2. B)Sodium bicarbonate administration to alkalinize urine and enhance renal lithium clearance
3. C)Loop diuretic (furosemide) to increase glomerular filtration rate and promote lithium elimination
4. D)Therapeutic plasma exchange to remove lithium from the intravascular compartment
5. E)Observation with frequent lithium level monitoring, as neurologic symptoms resolve spontaneously within 24–48 hours