A 56-year-old lady, who is a known case of lung cancer, presents with vomiting, headache and seizures. Investigations reveal serum osmolarity of 265 mosm/L (normal is 285-295 mosm/L) and a serum sodium level of 125 mEq/L (normal value is 136-152 mEq/L). Urine osmolarity is greater than 100 mOsm/L She has normal water intake. Which of the following drugs is useful for this patient?

Hyponatremia, Hypoosmolarity and inability to form dilute urine in the fully hydrated condition with concomitant lung cancer points to suspicion of SIADH. Antagonists of ADH are used to treat SIADH Tolvaptan - It is a direct ADH receptor antagonist. It is used for the correction of water retention and hyponatremia occurring in syndrome of inappropriate ADH secretion (SIADH) as well as in advanced CHF.