Can a pill restore sodium balance in patients with hyponatremia?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Hyponatremia in euvolemic or hypervolemic states, defined as serum sodium \< 135 mEq/L prior to randomization. 2. Able to give Informed Consent. Exclusion Criteria: 1. Women who are breast feeding and females of childbearing potential who are not using acceptable contraceptive methods. 2. Hyponatremia in hypovolemic states. 3. Acute and transient hyponatremia associated with head trauma or post-operative state. 4. Hyponatremia due to uncontrolled hypothyroidism or uncontrolled adrenal insufficiency. 5. Cardiac surgery within 30 days of potential study enrollment, excluding percutaneous coronary interventions. 6. History of a myocardial infarction within 30 days of potential study enrollment. 7. History of sustained ventricular tachycardia or ventricular fibrillation within 30 days, unless in the presence of an automatic implantable cardioverter defibrillator. 8. Severe angina including angina at rest or at slight exertion and/or unstable angina. 9. History of a cerebrovascular accident within the last 30 days. 10. Subjects with psychogenic polydipsia may not be included, however subjects with other psychiatric illness may be included. 11. Systolic arterial blood pressure \< 90 mmHg. 12. History of hypersensitivity and/or idiosyncratic reaction to benzazepine or benzazepine derivatives (such as benazepril). 13. History of drug or medication abuse within the past year,or current alcohol abuse. 14. Uncontrolled diabetes mellitus defined as fasting glucose \> 300mg/dL. 15. Urinary tract obstruction except benign prostatic hyperplasia (BPH) if non-obstructive. 16. Previous participation in another clinical drug trial within the past 30 days. 17. Previous participation in this or any other tolvaptan clinical trial. 18. Terminally ill or moribund condition with little chance of short term survival. 19. Serum creatinine \> 3.5 mg/dL. 20. Serum sodium \< 120 mEq/L with associated neurologic impairment, ie, symptoms such as apathy, confusion, seizures. 21. Patients with progressive or episodic neurologic disease such as multiple sclerosis or history of multiple strokes. 22. Child-Pugh score \> 10 (unless approved). 23. Patients receiving intravenous fluids at a rate greater than KVO (Keep Vein Open). 24. Hyponatremia due to lab artifacts. 25. Patients receiving AVP or its analogs for treatment of any condition. 26. Patients receiving within 7 days of randomization other medications for treatment of hyponatremia specifically: Demeclocycline, lithium carbonate or urea. 27. Patients likely requiring intravenous (IV) saline for correction of symptomatic or asymptomatic severe hyponatremia during the course of the study. 28. Severe pulmonary artery hypertension. 29. Hyponatremia should not be the result of any medication that can safely be withdrawn.