A 42-year-old woman is brought to the emergency department with confusion, nausea, and seizures. Her medical history includes small-cell lung cancer, and she has been on fluid-restrictive therapy due to suspected syndrome of inappropriate antidiuretic hormone secretion (SIADH). Laboratory tests reveal: Serum Sodium (Na⁺): 118 mM (Low) Serum Osmolality: 265 mOsm/kg (Hypotonic) Urine Osmolality: 500 mOsm/kg (Concentrated) Which of the following is the most appropriate initial treatment for this patient?
