"1. Women who are pregnant, breast feeding, or of childbearing potential who are not using acceptable contraceptive methods (such as barrier contraceptives or methods that result in a failure rate of less than 1%).
2. Patients with hyponatremia in hypovolemic states, defined as the presence of clinical and historical evidence of extracellular fluid volume depletion, including but not limited to skin turgor, orthostatic changes in blood pressure (BP) or heart rate (HR), dry mucous membranes, or a response to i.v. saline challenge.
3. Patients unable to sense or respond to thirst. 4. Patients who are likely to require prolonged hospitalization for reasons other than chronic heart failure (CHF), e.g. new femoral fracture surgery requiring extended recovery.
5. Patients with recent prior treatment for hyponatremia, such as hypertonic saline (within 8 h, just before the administration) or urea, lithium or tolvaptan (within 4 days, just before the administration) .
6. Patients with severe hyponatremia symptoms requiring immediate intervention with hypertonic saline; or who are expected to require such therapy within 48 h after randomization.
7. Patients with causes of neurological symptoms, which are attributable to psychological (psychoses), structural (dementia of the Alzheimer's type, post-infarct dementia) or other metabolic causes (e.g. hyper- or hypo- oxemia, glycaemia, calcemia, ammonemia, etc.) 8. Patients with acute and transient hyponatremia associated with head trauma or severe neurological injury (e.g. stroke, subdural hematoma).
9. Patients with a history of hyponatremia known to be due to severe, untreated hypothyroidism/adrenal insufficiency.
10. Patients with psychogenic polydipsia. 11. Patients with systolic BP < 90 mmHg at screening. Note, if it is confirmed under the BP<90mmHg at the first attempt, in addition, conduct a test twice more. And if it fits two results out of three in the criteria, the subject can be enrolled.
12. Patients with a history of hypersensitivity and/or idiosyncratic reaction to benzazepine or benzazepine derivatives (such as benazepril), or tolvaptan.
13. Patients with a history of drug or medication abuse within the 3 months prior to screening, or current alcohol abuse.
14. Patients with uncontrolled diabetes mellitus defined as glucose > 300 mg/dL (16.7 mmol/L) without regard to meals.
15. Patients with a current urinary tract obstruction (e.g. obstructive benign prostatic hypertrophy).
16. Anuric patients. 17. Patients with a serum creatinine > 3.5 mg/dL at screening. 18. Terminally ill patients or patients with a moribund condition who have little chance of short-term (e.g. 30 day) survival.
19. Patients whose hyponatremia is the result of any medication that cannot safely be withdrawn, such as anti-convulsants (e.g. carbamazepine) and anti psychotics (e.g. haloperidol).
20. Patients receiving desmopressin within 2 days of screening. 21. Patients who have participated in another investigational drug trial within the past 30 days(except for Non-interventional study).
22. Any patient who, in the opinion of the investigator, would not be able to comply with the study drug administration or study procedures, or whose overall medical condition would prohibit their participation in the study. (ex, severe pneumonia, infectious disease and etc.) 23. Patients treated and/or to be treated with strong cytochrome P450 (CYP) 3A inhibitors (clarithromycin, ketoconazole, itraconazole, ritonavir, indinavir, nelfinavir, saquinavir, nefazodone, telithromycin).
24. Patients with rare hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose- galactose malabsorption.
25.Patients with Aspartate transaminase(AST) or alanine transaminase(ALT) >2.5 times the upper limit of normal(UNL), total bilirubin > 2mg/dL or who under any medication treatment for liver disease at screening"