<prompt> 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 mosmL normal is 285-295 mosmL and a serum sodium level of 125 mEqL normal value is 136-152 mEqL. Urine osmolarity is greater than 100 mOsmL She has normal water intake. Which of the following drugs is useful for this patient?AcetazolamideHydrochlorothiazideTriamtereneTolvaptan  <response>: 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. 